Jacek Rzeuski currently lacks the time to continue work on Directory Opus 4. Here's Jacek's original Statement:
The development is on hold and I have no idea when I'll resume it. The GUI changes towards BOOPSI are only partially completed and I stuck on handling RMB on bankbuttons. Intuition doesn't pass RMB clicks to BOOPSI gadgets so I have to find a way to emulate it and notify gadgets manually.
If someone needs an updated version for AOS4 or even a native AOS4 version then feel free to get sources from the CVS at sourceforge.net then modify and compile them. The BOOPSI changes are not committed to the CVS so the sourcetree should compile and work."
If you'd like to have a go at compiling (or even improving) Directory Opus, it might be a good idea to subscribe to our mailing list, as at least one or two people are already trying to compile the CVS source tree. Note that the CVS only contains the sources for Pre19, the sources for Pre20 and Pre21 are lost...