Zulip doesn't have a strong dependency on Ubuntu 14.04.
It would be less than a day's work to have it support any additional version of Debian or Ubuntu (precise/wheezy would be quite easy since we've run both in production). It's probably also not hard to support something RHEL-based too but that'd be a bit more work.
RAM usage could also be brought down a lot for smaller environments with a bit of work; most of it is the fact that we run a set of like 15 queue processing workers that each import the entire application.