I like Kenny's FOCUS acronym simply cause it has the best branding potential so far... things like Pueblo and Agora are a little esoteric--they have to be explained.
I really love the "Open" part of OpenACS. I think that part is critical, plus it is likely that a URL like www.open???.org would be available.
So I was thinking of things like:
openfocus (but the open part is redundant in the acronym)
openagora (but again... agora is such a general term)
opencs (Open Community System- bland, but clear)
openct (Open Community Toolkit)
My mind seems to be taking this down the bland path... anyone have more interesting open??? names?