With the recent mania over Web 2.0 and one of it's common bretheren, AJAX (BTW, Web 2.0 doesn't specifically dictate AJAX), there has been quite a proliferation of JavaScript frameworks (and frameworks built upon frameworks): prototype, moo.fx, MochiKit, DoJo, and more.

I just discovered f(m), which is, in the creators' words, "an ECMAScript Base Class Library, based on the .NET Framework, that was written to serve as the foundation for a new breed of browser-based Web Applications".  To clarify, ECMAScript is the official spec that JavaScript follows (since it was created based upon JavaScript).  And, I assume by "Base Class Library", they basically mean "framework".

What does "based on the .NET Framework" mean?  Well, at first blush I thought they mean some sort of server-side C#/VB.Net classes that generate  client-side Javascript functionality on the fly.  Nope.  They mean a JavaScript framework literally styled after the .NET Framework APIs.  In other words, classes in JavaScript such as System.Collections, System.Text, System.Events, etc.!  An awesome concept for a .NET developer -- or anyone else, for that matter, because the .NET API layouts are well thought-out, being the child of a 600 pound gorilla.

I haven't used it personally, but it looks VERY promising!

Check it out: f(m) : ECMAScript Base Class Library