Discussion on designs for new language features and other user-facing language changes. Home of the language design team.
Discussion around libraries, either in the community or officially supported (hosted by
Discussion about the compiler itself -- internal data structures and algorithms, optimizations, parsing, and so on. Home of the compiler subteam.
Low-traffic category for announcements about the decision making process, such as when RFCs are entering the final comment period, new meeting minutes are available, and so forth.
Discussion about all "official" (rust-lang managed) non-rustc tools, and community infrastructure:
Discussion about the documentation, either the prose docs or the API docs.
Community happenings, such as talks, meetups, group projects, etc.
Discussion about this forum, its organization, how it works, and how we can improve it.
Discussion about the Rust Guidelines. Available rendered here and as source. Use the "style" subcategory as appropriate!