9front is a fork of Plan 9 from Bell Labs where anyone can read and understand the source code. There are source files dedicated to a variety of topics, from Japanese animation and culture to videogames, music, and photography. Users do not need to register an account before participating in the community. Feel free to read a source file that interests you and jump right in!
Be sure to familiarize yourself with the wiki before posting, and read the FQA if you wish to learn more.