Prototype is an open-source JavaScript framework that smooths over the rough edges of cross-browser development so you can focus on writing kick-ass web applications.
Not long ago, I tagged Prototype 1.7.1, an update 18 months in the making. It features an overhaul of our DOM library and better coexistence with ES5 methods, but quite a bit more as well.
Prototype takes the complexity out of client-side web programming. Built to solve real-world problems, it adds useful extensions to the browser scripting environment and provides elegant APIs around the clumsy interfaces of Ajax and the Document Object Model.
Getting started: Defining classes and inheritance • How Prototype extends the DOM • Introduction to Ajax • Using JSON • Event delegation • Using Element.Layout