Hyperschema.org is a site that consists of a library of core hypermedia definitions along with schemas for many hypermedia formats. You can find the source on Github.
The purpose of this project is to provide a vocabulary for describing hypermedia formats. From this vocabulary, hypermedia formats can be validated and extended and new formats can be created and documented. Additionally, the hope is that this project provides a foundation for hypermedia clients that can understand many different hypermedia formats.