This is the Directory Opus 4 source code.
Jonathan Potter writes: The release of Directory Opus 4 under the GPL in NO WAY affects the existing
commercial status of Directory Opus 5. [..] The source code is largely uncommented, messy, spaghettified, and generally in bad shape. I sincerely recommend you consider upgrading to Directory Opus 5, the source code of which is _much_ better :)