Zepto.Js is pretty light weight with lots of features and is easy to use. It's not the prettiest, but it's not a bad library, either. The documentation is pretty good, and the developers are very active on the forums. The library is very easy to use and has all of the tools you need to build robust applications. There are lots of cross browser issues, and it's not always clear what the intended behavior is for a given situation. The documentation isn't always up to date, and I've had to look things up in the source code to figure out how to do things. The library is easy to use and very well documented. It's great for small applications, and it's easy to add features.