DOWNLOADDownload Ouka Chat Server
Ouka Chat Server is free to use. You can download latest release from the download archive (note that some releases are to be considered as beta/test versions).
Oukas forum is japanese, but the archive will give you what you need.
(The E in the file name indicates it's an english version. The oposite case will be J for Japanese version.)
Download Ouka Help File
The help file can be downloaded from here as a standalone help file. The file contains search and other advanced features.