A ton of open source hardware projects make their way onto Github, and Eagle is one of the most popular tools for these designs. [TomKeddie] came up with the idea of searching Github for Eagle files containing specific parts at Hacker Camp Shenzhen, and a method of scraping useful ones.
The folks over at Dangerous Prototypes used this to build the Github Hardware Search tool. Simply enter a part number, like “ATmega328P”, and you’ll receive a list of the designs using that part. You can then study the design and use it as a reference for your own project. You can also snag library files for the parts.
Of course, there are some limitations to this. The most obvious one is the lack of quality control. There’s no guarantee that the design you find works, or has even been built. Also, it only works for Eagle 6+ files, since prior versions were not XML. You can read more about the design of the tool over on Dangerous Prototypes.