It's currently Oracle-only.
When it is fully ported to OpenACS 4.x, it will run under either RDBMS.
Furfly did the ACS Classic [oracle] 3.x -> ACS Classic 4.x.
Civilution people and Walter McGinnis (who contracted with furfly for the 3.x->4.x step) will do the ACS Classic 4.x -> OpenACS 4.x (oracle and PG).
Furfly and Civilution both have a vested interest in seeing this happen, as they both build custom websites for clients.
