The word that comes to mind for me is "toolkit". I see OpenACS as a toolkit for building collaborative and ecommerce websites.

I think Agora would have been perfect, but since W-Agora is already taken, I don't want to encroach on their name. I would have killed to see the Agoraphobia FAQ.

Pueblo is a good name, and is memorable.

I liked Communikit also, because it sounds like Communicate and Community Kit at the same time. It implied a toolkit for me.

Another attribute of ACS is rapid development. It seems like it doesn't take very long to build a full-featured site.