When development of Kusaba stopped, a copy of the source was hosted here so that others could grab a copy and fork the project. This was due to the fact that it was the easiest PHP-based imageboard software to use at the time, as well as being the only one to have a centralised management console.
Since then, there have been several forks, including Kusaba X and Kusaba 2, however there have been several other projects started as well. For example, Trevor created PyIB (a Python-based replacement for Kusaba) and another group is developing Tinyboard, which has one or two interesting ideas. As such, there is no real need to host the Kusaba files anymore.
In the meantime, why not visit one of the boards?