Hi everybody,
Looks like the others are getting closer:
Gmail like AJAX powered Web 2.0 version of IMP http://janschneider.de/news/25/252
Duroty System (BETA) is the open source Gmail http://www.duroty.com/en/index.jsp
The main problem of RoundCube is the project manager's lack of time and as a consequence of that the bad project organization, both my faults. If somebody thinks he or she could afford some time (actually it's a full-time job) and who has some experience in project management, I'm willing to give away the "power" and become a regular developer (that's what I really am).
Regards, Thomas