Prototype is a JavaScript library that aims to ease development of dynamic web applications. Its development is driven heavily by the Ruby on Rails framework, but it can be used in any environment.
This was the way the README described Prototype whose version 1.0 was released in March of 2005 as simple set of functions (most of them famous today) in around just 335 lines of code.

The origins of Prototype are shrouded in mystery. Though Prototype has evolved considerably over the last years.

This section cover also information about Scriptaculous framework: a library that makes use of Prototype to deliver a rich set of high-level functionality to work directly in creating polished interactive user interfaces