Admiral Adama: "Launch All Vipers, I got mah eatin' britches on"
An atlas, in architecture, is a support or column sculpted in the form of a man; the plural is atlantes. Another name for such a column is telamon (plural telamones or telamons, Caryatid is the female equivalent.). In Microsoft parlance, "ATLAS" is the new server-side to client-side architecture that lets you "AJAX" (remote scripting) - enable your ASP.NET 2.0 applications. (AJAX, of course is a foaming cleanser or a soccer league).
Up until now, I've stuck with either Anthem.NET or MagicAjax (both can be found on SourceForge.net), the two open-source infrastructures that feature the preservation of the stateful page object during client callbacks without reliance on external handlers (unlike another popular one, "AJAX.NET" - which does not do this.) Both are easy to learn and both support ASP.NET 1.1 and ASP.NET 2.0
However the Atlas offering is shaping up to be much more mature - with a complete declarative markup set of controls for progress, UpdatePanel, etc, and a fully fleshed -out API.
This new March CTP is accompanied by a reworked site, and some nice viewable videos. Be sure to watch the one by Scott Guthrie on his "TODO List" - you'll be hooked -- he puts together an entire ASP.NET 2.0 application and ATLAS - enables it, literally from SCRATCH, in less than 18 minutes! There is also complete online API documentation (albeit still "beta") along with a lot of walk-through samples.
And, above all - it offers GOLIVE license permissions which essentially means you can start using it "for real" in your public web sites.
Snag yourself a copy of the downloads here.
All-in-all, this is what I would characterize as a pretty ambitious project - the Microsoft.Web.Atlas.dll assembly is 1864K! The good part about all this effort is that developers will be able to "ATLAS-Enable" web sites using familiar ASP.NET declarative control syntax and events (or you can get "under the hood" if you want with the API) - which means that the learning curve is pretty easy.
Of course, a lot of that depends on your "frame of reference" -- for example I just read where a coyote was found roaming in Central Park (it was captured). When I mentioned this to a co-worker, he responded "How on earth did a coyote get into Central Park!". My frame of reference being that of a native New Yorker, I quipped, "I guess he came down from the Bronx.".
Fawlty Math Department
EU: "Hey MS, how much is 2+2?"
EU: "I don't understand."
MS: "2 + 2 = 4"
EU: "I disagree! how much is 2+2?"
EU: "What about the documentation you promised? Now how much is 2+2?"
MS: "We will leave no stone unturned to overcome the compliance impasse. 2+2 is 4."
-- Get the picture?