Forum OpenACS Q&A: Response to Open ACS kernel + ACS modules
ACS 4.x is actively under development by ArsDigita, but we are currently developing it for J2EE and not AOLserver. ACS 4.6 is released today, and is available here. Our plans for development of the colloboration modules are here. Any code written with ACS 4.6 will be supported in the 5.0 upgrade.
Postgres support is planned immediately after the 5.0 release. 5.0 is currently scheduled for release in October. I'll be happy to answer any questions you have about the system.