Ideal for begginers in AJAX (like me):

http://simplejs.bleebot.com/
SimpleJS is a javascript library simple and light proposing functions ready with the use to facilitate the exploitation of ajax.

Developed primarily for the beginners and the small projects, SimpleJS is a library without claim and donot can in no case to be compared with Prototype or another professional framework.

SimpleJS weighs 14kb and does not require any external framework. The functions are very simplified.