Windows Server code name “Vail” is the name for the upcoming version of Windows Home Server. It will be based on top of Windows Server 2008 R2 and feature a complete new server console (now called Dashboard). A preview version of “Vail” (ctp4, community technology preview 4) with the buildtag 6.1.7360.0 (hsbs_ids.091210-1540) leaked to the internet in late January.
For an in-depth overview of the leaked Vail build, check this post by Rafael Rivera.
As you can see on the graphic below, private testing of Vail begun in 2009 and a public beta should be around soon. Microsoft has not announced a release date for Vail yet, but probably it should be available together with “Aurora” in the first half of 2011.

Windows Server code name “Aurora”

Windows Server code name “Aurora” is the name for the next version of Windows Small Business Server. Aurora will also be based on Windows Server 2008 R2. Not much is known about it yet, but there seems to be a build with the tag 6.1.7408.0 (hsbs_main.091216-2300). Aurora should also be available in the first half of 2011.

Update (4. Feb, 2010): I asked the owner of the server on which I have found the first Aurora bits (wanderingkiwi.com) about a possible date of a public beta and got this answer:

Unfortunately you have stumbled across one of my test servers at home.  I work in Windows Server at Microsoft. I wish I could tell you more, but at this time we are not ready to discuss future products but will certainly let you know as soon as more details become available.

Here is another answer I got from a Microsoft employee regarding Aurora:

We are not ready to discuss future products, but will certainly let you know as soon as more details become available.

Windows code name “Colorado”

“Colorado” is the code name of the new Client Computer Connector of Vail and Aurora. Since both, WHS and SBS are developed by the same team now (hence the hsbs in the build tag, hsbs stands for Windows Home and Small Business Server Team) the Client Connector is the same (also the remote interface of both looks pretty much the same at this point).

Update 2 (10 Feb. 2010): Recently a new version of the Client Computer Connector leaked (build tag is 6.1.7447.0 (hsbs_main.100207-2200)). It does not show the “Colorado” in system properties anymore.

Update 3 (17 Feb. 2010): A few more Client Computer Connectors leaked. Here is a list of all currently known Vail/Aurora builds:

6.1.1224.0 (wssg_common.090723-0400)
6.1.1308.0
6.1.1326.0 (wssg_common.091105-0400)
6.1.1329.0 (wssg_common.091110-0400)
6.1.1335.0
6.1.1336.0 (wssg_common.091119-0400)
6.1.1340.0 (wssg_common.091125-1800)
6.1.1345.0 (wssg_common.091203-0400)
6.1.1346.0 (wssg_common.091204-0400)
6.1.7360.0 (hsbs_ids.091210-1540)
6.1.7408.0 (hsbs_main.091216-2300)
6.1.7434.0 (hsbs_main.100125-2200)
6.1.7444.0 (hsbs_main.100204-2200)
6.1.7447.0 (hsbs_main.100207-2200)
6.1.7451.0 (hsbs_main.100211-2200)

(those in italic have been found in the leaked Vail CTP, it’s not clear whether these are Vail builds or not)

Windows Home Server / Small Business Server Support Lifecycle

Windows Product Roadmap

Finally, here are some wallpapers I made:

"Aurora" wallpaper

"Vail" wallpaper

"Aurora" / "Vail" bliss

There are 3 kinds of these developer builds, which are:

IDW – Internal Developer Workstation
IDS – Internal Developer Server

Originally the IDS term was used to describe a build which can be used as a server and the IDW term was used for a build which can be used as a workstation inside Microsoft “without too much pain”. Later, this connotation has changed and these builds have been seperated into two “tiers”: IDW for unstable builds and IDS for builds which are a bit more stable than IDW builds, but not as stable as beta builds. IDS builds did not have to be a Server SKU anymore (and vice versa).
Today, the term IDW is used for CTPs and stuff like this and the term IDS is used to describe unstable builds, or builds of a “helper-branch” (for example winmain_win7ids).
The term IDX (Internal Developer Client/Server) is used to avoid confusion between IDS and IDW.

Here is a quote a guy from the WSSG (Windows Server Solutions Group) made once:

This milestone is termed the “Internal Developer Server” (IDS) build – it’s
an internal quality term we use meaning that the build is stable enough to
deploy and evaluate, but may contain more minor bugs than a Beta build.
You’ll run into some unedited UI stings, and some bugs that we purposefully
chose not to fix until later in the development cycle. It’s a tradeoff we’ve
made to ensure we keep getting great feedback without unduly delaying the
project.

EDW – External Developer Workstation

This term was used during the final development of Windows Vista (between RC and RTM) for builds which got released to the TAPs. I am not sure if this term has been used for anything else, but I think you can compare this with the IDX builds of Windows 7 (which represent something like an inofficial/internal Release Candidate).

Let me know if you have any anything to add.

What are Escrow builds?

(Update from 10. Jan, 2010)

Sometimes Microsoft released builds referred to as “Escrow”. Escrow means the development of a branch gets stopped and the code is being tested. If Microsoft or its testers don’t discover any serious bugs (“showstoppers”), the current build becomes the final milestone (usually RC or RTM, but sometimes there are also beta escrow builds). Escrow builds are usually handed out to TAP (Technology Adoption Program) testers, ISVs, IHVs, etc.