Wakaba and Kareha are my attempts at implementing from scratch image and message boards of a type popular in Japan (used on sites such as Futaba Channel and 2channel). This kind of board software is built around anonymous posting and no requirements for registration, to make the boards more suited for casual uses, and more fun overall. They are written in Perl, and are designed to be more efficient and cleanly written than the original scripts that are available, while preserving the same kind of functionality. Both scripts are in use at iichan, an English-language site built along the same lines as the Japanese Futaba Channel, and also 4-ch, an English-language discussion BBS.
Kareha is a message board script. It is more loosely modelled after the sort of message board scripts used on 2channel and many other similar sites. It tries to use modern structured XHTML and CSS layout. It does not need a database backend either. Shii, who has his own similar message board software written in PHP, has written a nice summary about what's so good about this style of message board (mirrored here as he has pretty much given up on the project).
I used to have a script called Wakaba Zero, which was an implementation of Wakaba that did not require a database, but Kareha has now gained enough functionality to take over this role. Those who want to run an image board but do not want to bother with databases can use Kareha to run a Wakaba-like board.
There is also a somewhat incomplete documentation wiki, which contains a bit of information about the scripts.