Transitioning to Blender 2.8

UPDATE:  As of November 29, 2018, Blender 2.8 is now in open BETA status!

This thread will be a list of information that I and others have found while exploring the alpha builds of Blender 2.8, that may be of use to established users of Blender 2.7x and previous versions in transitioning from the old to the new version. While the functionality and general layout of Blender 2.8 is substantially the same as in previous versions, there are some important and dramatic changes that may present extra challenges for experienced Blender users who are used to the way things have been up until now.   This OP used to live on page 4 of the BC1-1808 August Class thread; but it was somewhat buried there, and I figured a dedicated thread which could be bumped to the top of the forum from time to time would make the information a lot more discoverable, especially for newer people.

As was the case during the alpha, new Blender 2.8 Beta preview builds are released daily - sometimes more than once per day - and can be downloaded at this page. Since Blender 2.8 is a work in progress, everything in this thread is subject to change. I would like to do things like add screenshots of different UI elements; but that will probably have to wait until 2.8 is closer to its final version - the fact is, UI elements, icons, layouts and such are still changing from time to time, often enough that there's just too much risk that screenshots and highly exact information will quickly become outdated and keeping up with all that would be a chore.

Anyone is welcome to post changes they've found in this thread.  Feel free to discuss changes, announcements, and link articles and videos about new features of 2.8 as you learn about them.  If you find videos that explain some new features well, by all means post them!  This OP will contain the "main list of changes" and I'll try my best to update it periodically as new features or changes happen. I will add things that others find too, so that people don't necessarily have to read the entire thread to get all the information (I'll credit these additions).  These updates won't happen every day though - so if you're going to explore 2.8, be prepared for new and unexpected things.

So, on with the changes.

1. User Interface

• NEW 11/29: By far the most substantial change is that BLENDER 2.8 IS NOW LEFT-CLICK-SELECT BY DEFAULT.  In this mode, left-click will select and perform actions, while right-click will call a context menu relevant to wherever you right-clicked, as in all other Windows programs you are familiar with (presumably Linux as well).  Right-click-select mode functions as it always has, but is no longer the default setting.  
• Whether you are in left-click-select mode or right-click-select mode, clicking to "select" nothing/empty space in the scene, will de-select all objects.
• Aside from that, the biggest changes will be instantly visible when you start Blender 2.8. The first thing you'll notice is that by default, the 3D Viewport's header is now at the top instead of the bottom, and is also partly transparent. You can still move it to the bottom if you want by right-clicking in the header and choosing "Flip to Bottom". If you open a pre-2.8 Blender file in 2.8 and have "Load UI" checked, the header will automatically be at the bottom of the 3D viewport. The positions of some controls in the header have changed.  On the right side of the toolbar, you'll find viewport shading and overlay options that used to exist in the Properties panel and have been expanded upon with "popover" menus.  These controls have been fiddled with a lot over the course of the alpha, so I don't want to spend too much time describing them yet - exploring them on your own will familiarize you with them quite easily.
• In the upper right corner of the 3D view, there is a Navigation Widget.  This is intended mostly for beginners, but might also be useful for those using Blender on a tablet.  You can click and drag on the colored axes to orbit your view, or click on a specific axis button to snap the viewport to that view.  Clicking and dragging on the magnifying glass dollies your view in and out; clicking and dragging on the hand pans your view.  You can also toggle Camera View and ortho/perspective modes using the appropriate widget buttons.  You can turn this widget off completely by going to User Preferences > Interface and changing "3D Viewport Axis" from Interactive Navigation to Simple Axis, which will replace the widget with a 2.7x-like simple colored axes display. 
• The toolbar, aka "T-panel", is very different; the tool buttons are much larger and have icons, but they still change according to the Mode of the viewport. Unlike when you use a hotkey, which only makes a tool active until you complete an operation, a tool selected by clicking in the toolbar, will remain active until you select a different tool (the Select and Cursor tools can be considered the "neutral" options). 
• The Properties panel (the "N" panel) is mostly the same, except for the relocated display options. The panels can still can be toggled on and off using the T and N keys. Both of these panels are also partially transparent; you can get rid of the transparency in the User Preferences (System > uncheck Region Overlap). User Preferences is now in the Edit menu instead of the File menu, which is more consistent with most Windows programs, and as of 11/29 is now called Settings.
• You can scale the size of buttons and other controls in the Toolbar and N-panel by holding Alt-MMB and moving the mouse up and down (if you didn't know, you can do this in 2.7x as well). You can also scale the size of the controls in the Properties Editor the same way.  On the toolbar specifically, you can click and drag on the right side of it, to hide or show the tools' text labels. 
• NEW 11/29 - by default Spacebar now toggles Playback.  In the Settings, you can instead set the Spacebar to bring up the search function, as in 2.79, or tool selection menu at your mouse cursor.
• The default Search hotkey is F3.  Weirdly, in 2.7x, both the spacebar and F3 launched Search; a lot of the keymap changes in 2.8 eliminated redundant or overly-complicated hotkey assignments like that.  As mentioned above though, you CAN set the Spacebar in the Settings to call Search as in 2.7.
• The Tool Options for sculpting and texturing brushes, which used to live in the 2.7x T-panel, now live in the Properties editor. It has a new tab in the icon list, the Tool tab, and the tool options will be there.
• The Properties Editor's tabs are now arranged vertically down the side, rather than horizontally across the top.  This eliminates the weird MMB-drag horizontal scrolling object in the otherwise all-vertical window, so it makes logical sense, but it might still take some getting used to.  The tabs are in basically the same order, although there are a couple of new tabs.
• Output settings have been removed from the Render tab and now have their own Output tab, which is just under the Render tab in the tab icon list.
• When you start to use an operator, the appropriate floating Operator Panel - the one you used to have to call up by tapping F6 - now appears in the viewport automatically. There is no docked panel in the Toolbar anymore.
• The ~ key calls a Views pie menu, that allows you to switch between views in the same way as the numpad, without having to use your mouse-hand to hit the keys.  If you have learned which view is where in the pie menu, you can move the mouse in the direction of the desired option immediately after pressing ~, like a "gesture", and the viewport will instantly flip to that view without you having to actually click.  All pie menus have this gesture-like functionality, by the way!
• In 2.7x, each editor had little triangle-handles in the bottom-left and top-right corners, that you could use to collapse or drag out new editor windows. In 2.8, the triangles are gone; there are no visible handles, but you can now click on ANY corner and perform the same functions (the mouse pointer turns to a small crosshair when hovering over those areas). This also includes holding Alt and click-dragging over an adjacent editor to swap the two editors. Right-clicking between windows still gives you the split and join options as before.
• WIREFRAME MODE IS BACK!  Under the hood it is different; but the devs have fixed things so that now turning it on functions visually the same way it did in 2.7x.  You can adjust things like edge brightness or transparency in the display settings on the header bar.  Toggle Wireframe mode using Shift-Z.
• SUBDIVISION SURFACE MODIFIER NOW FULLY WORKS IN EDIT MODE!  
• MULTIRESOLUTION MODIFIER FOR SCULPTING NOW FULLY WORKS!
• At the very top of the screen, you will notice the Workspace tabs.  This is one of my favorite new features of 2.8.  They replace and improve upon the little-known Layouts function from 2.7x.  Workspaces are pre-defined screen layouts tailored for specific tasks as labeled - like Sculpting, UV Editing, Compositing, and so forth.  For instance, clicking on the Sculpting workspace hides the timeline, puts your 3D viewport into Sculpt Mode, assigns a matcap to the selected object, and sets your Properties editor to the Tool Settings tab - you are instantly ready to begin sculpting without having to do anything else to your UI.   Having these workspaces available makes it easy to switch between different kinds of work without constantly having to tweak and tug and switch UI elements as your workflow progresses; you can just switch back and forth between the different tabs as needed.  The Workspace tabs are already arranged in a logically common project workflow order and are well-designed; but of course the tabs can be rearranged, renamed, deleted, or new Workspace tabs created and added as you like.  The Workspaces themselves are completely customizable, and retain things like editor modes and selected options.  I personally find Workspaces extremely useful.
• In 2.8, you can Edit multiple objects' meshes at once.  Just select as many as you want and enter Edit Mode as normal.  BLACK MAGIC!
• 11/26: LOCAL VIEW IS BACK!  It still uses the slash ("/") key.  One important difference from behavior in 2.79 is that in 2.8's local view, your selected object(s) will no longer be lit by lamps in the scene unless you also add those lamps by having them selected when you enter local view.  This should only be a problem if you're actually trying to render from local view; viewport lighting in Solid and Lookdev modes will still be there as normal.

2. Hotkeys (note, of all the recent changes in 2.8, hotkey assignments are the most susceptible to being changed again before the official release)

• When you launch 2.8, the splash screen has a drop-down box that lets you choose the 2.7x-style keymap if you want to use that.
• By default, the A key is Select All and Alt-A is Deselect All.  NEW: You can change this back to a toggle with just the A key like in 2.7x by going to the User Preferences > Input tab and ticking "Select All Toggles".
• Alt-A no longer starts and stops animation playback. Shift-Spacebar does that now.
• The Q key opens an editor-specific Favorites menu that is customizable by you. You can right-click on practically ANY button, option, even whole entire menus, in Blender and add them to your Favorites menu. For instance, in Object Mode you can go to the Object menu and right-click Smooth Shading and add it to Favorites. Or, you can just right-click add the whole Object menu to Favorites as an expanding menu. Or, you can straight up add Object Mode itself to Favorites, if you want to.  The Favorites menu is also contextual, meaning for instance what's in your Q menu when you're in Object Mode is different from what's it in when you're in Edit Mode; and what's in it when your mouse is hovering over the Outliner instead of the 3D Viewport is different still.
• As mentioned above, F3 rather than Spacebar directly brings up the Search tool.
• While in Edit mode, the 1, 2, and 3 keys in your number row (NOT the numpad) will switch between vertex, edge, and face select modes.
• The hotkeys for some of the Sculpting brushes may have changed.  You can see all the hotkey assignments for the brushes by using Spacebar to call the tool menu while in Sculpt Mode.
• ADDED 11/26: Ctrl-Tab switches a Dope Sheet editor to a Graph Editor, and vice-versa.  No more need to crowd your screen with both these editors at the same time, or keep a tiny one in a corner to drag and swap.  

3. Collections

• The big one. Collections is the new system in 2.8 that has replaced the old Layers and improves upon them. Collections live in the Outliner. Like Layers they can be made visible or invisible; unlike Layers, they can also be named, rearranged, made deselectable, nested inside other Collections, and objects can belong to more than one Collection at the same time.  Organization is awesome.
• The M key that formerly allowed you to Move objects to other layers, now allows you to move them to other Collections in the same way, or to create new Collections to put an object in. No need to adjust to a new hotkey there!
• If you open a 2.7x or previous Blender file in Blender 2.8, the existing layers in that file will automatically be converted into Collections, that will be named relatively - for example, everything that was in Layer 1 will now be in "Collection 1", while everything that was in Layer 11 will now be in Collection 11. Of course you can rename the Collections as desired.  It should be said here that while 2.8 is coded to recognize layers and convert them into Collections, 2.7x does not have reciprocal functionality.  This means that you can open your Blender 2.7x projects in Blender 2.8, but not vice-versa.  Likewise, once a former 2.7x project opened in 2.8 is saved, it becomes a 2.8 file and cannot be opened again in 2.7x.  Plan accordingly if you intend to experiment with old projects!
• For the purposes of LINKING and APPENDING from other Blend files, "Groups" in older files are now recognized as Collections by the 2.8 File Browser. Linking and Appending works just fine; I've tried this with the Vonn Bots and had no problems. As mentioned above, Collections will be generated as necessary in place of layers.  Linking or Appending something from a 2.7x project into a 2.8 project will not ruin the 2.7x file, don't worry.

The above is really all you need to know to use Collections in the same way as you used layers in 2.7x. Of course Collections are a little more powerful than that; I might post a more in-depth treatment at some point, or a video if I find a particularly well-made one. 

4. Grease Pencil

The Grease Pencil tool as it existed on 2.7x is now called Annotations.  It is selectable in the toolbar in Object and Edit Modes and the settings can be found in the N-panel and the Tool Settings tab in the Properties editor.

The name "Grease Pencil" in 2.8 now refers to a completely different, brand-new and complex 2D drawing and painting system for creating 2D animations in Blender.  There was nothing like it in 2.7x, and I'm afraid I don't know much about it or how it works, as I'm strictly a 3D person.  But, when I find an in-depth article or video tutorial about Grease Pencil, I will definitely post it here for the benefit of people who are interested in this hotly-anticipated new feature.

5. Addons

If you haven't checked on 2.8 in a while, you'll be pleased to learn that almost every addon included with Blender 2.8, now works and can be activated.  You'll remember that in the earlier days of the alpha, most addons were disabled - and could not be enabled - with the exception of a select few like Node Wrangler and some import/export addons.  Now, your IvyGen and your Archipack and your LoopTools and your Rigify all work and can be enabled.  That said, you will find that the list of included addons has been noticeably pared down and many are missing.  Extra Objects and Sapling, for instance, aren't there.  Presumably the creators of those addons will have to update and re-release them by themselves.