https://github.com/acdlite/react-fiber-architecture (overall architecture - follow links)
https://github.com/facebook/react/blob/master/src/renderers/ (official examples)
https://github.com/nitin42/Making-a-custom-React-renderer (tutorial + example)
https://github.com/iamdustan/tiny-react-renderer (tutorial + example)
https://github.com/manaflair/mylittledom/blob/master/sources/term/react.js#L232 (example w/ lots of comments)
https://gist.github.com/koba04/963c9b3d16b372d6420f397ae97c55a5 (example)
facebook/react#10758 (pending PR for building standalone libs)
https://github.com/facebook/react/pull/10813/files (tradeoffs doc)
Suggestion: replace
/master/
links with links to specific commit hashes (otherwise they are susceptible to 404 over time).