HackEDA has an online automatic circuit design that builds Eagle schematics and boards from predefined blocks. This is one of the great hacks now possible because Cadsoft switched to an open XML text format for board files:
At it’s core, it’s a system for collecting reusable-sized pieces of electronic designs, along with the knowledge necessary to reuse them in new designs. The library is available to browse online, you can download the individual bits, and there’s also a tool for creating custom circuits by simply selecting the features your project needs.
Via Hacked Gadgets.