fyi, Webvanta is built with Ruby on Rails, and a bunch of other stuff... It is a designed as a SaaS system and uses a cluster of servers running various things (nginx, clustered MySQL, and a few others). As noted above, there's some more details on the technology we use at www.webvanta.com/technology.

It mentions Postgres in the installation instructions. Works for me, although I suppose it's better if it's not tightly bound to one particular thing.