As far as Javascript frameworks go, it really is hard to beat Prototype by Sam Stephenson. Dubbed as a “framework that aims to ease development of dynamic web applications”, Prototype is quickly becoming the library of choice for Web 2.0 developers.

Several prominent web projects, currently rely on, or are heavily based on Prototype:

• Ruby on Rails
• script.aculo.us
• Rico
• Behaviour

* Look for reviews on each of these libraries very soon…

Although, AJAX is not the primary goal of the Prototype framework, it certainly has a very nice implementation. And through JavaScript classes, it also makes extended in your own projects, a piece of cake (relatively speaking of course).

Prototype is available here: http://prototype.conio.net