A tiny, super-lightweight image board written in PHP. Can use MySQL, Postgres, or SQLite as its back-end database, or you can fall back to flat files. Unusually configurable for an image board - you can make images optional in posts or even force no images at all. It's even still being developed.
A server-based chan like BBS written in C. No registration, just post. Supports tripcodes. futaba style. Aggressive content turnover. Requires lighttpd (probably) as its front-end, sqlite backend.
Kareha doesn't use a database, Wakaba does.