First one is basically is used for messages between Client and Server. This one is kinda broken, as in, not the best implementation I could do. So, beware.
The next one is a main feature of the entire library. It's a NetworkAPI that works with tubes/pipes. It uses an unweighted undirected graph based system to easily network together an entire network of, well, anything. If you don't like the implementation you can easily implement your own and plug it into the existing system, it handles the checking, such as "Is this pipe merging these networks", and it passes it off to your own implementation. It's insanely easy to do a pipe network.
Next up, it contains a massive framework for blocks and items, simply extend one of them, and you'll get access to a massive collection of useful methods. The best way to do this would be to create your own abstract class and extend one of mine, that way you don't have to keep on returning your Mod Id with every class.
It also contains a fairly extensive GUI system. That's still in development.