The ultimate reference for JSON tooling and specs.
If you're not familiar with JSON of course you want to check out json.org first. Then, go and have a look at the RFC4627 where the application/json
media type is defined.
Want to contribute? This site is hosted at GitHub as a GitHub Page so if you fancy extending the listing here simply send a pull request to jsonauts/jsonauts.github.com.
JSONaut is a wordplay: see Jason and the Argonauts.