The slogan of ender is Build only what you need, when you need it. Small decoupled modules allow a smaller size then other librarys. Ender provides modules like a Selection Engine, Ajax, Dom Manipulation and Animations.
It is easy to use, with expressive and familiar syntax. In order to get started watch the introduction video. If you need help with ender, twitter is your friend. Just use the tag #ender.
In the next article, you will learn how to install, setup it.