Feature-rich and lightning fast forums. Works standalone or as a Rails engine. Markdown by default, with plugins for code highlighting, KaTeX math, and BBCode. No JavaScript required. Easy deployment on Heroku or Ansible.
We wrote the Thredded forums engine focusing on these things:
1. Client-side performance. Little JavaScript and lean CSS. Even the KaTeX math plugin renders math server-side.
2. Clean but discoverable UI. The focus is content. No dropdowns / hamburger menus.
3. Extensible but critical features are built-in to provide a foundation for plugins. Features such as notifications, moderation, permissions system, and full text search.
4. Pleasant on mobile for both browsing and content creation. This means a textarea instead of a rich text editor (by default).
5. Everything degrades gracefully when JavaScript is off. For example, preview-as-you-type becomes a "Preview" button if JavaScript is disabled.
6. The relational database for everything, including full text search. Data integrity is easy, no out-of-sync elasticsearch databases here. Runs on Postgres, MySQL, and SQLite.
Boring technology => easy to deploy and run in production.
The codebase is written in Ruby, has slowly developed over the years, and has extensive test coverage.
I am very curious to hear what you think, and whether you've ever felt a need for a forum like that.
Thredded