(We're in the midst of an Oracle->Postgres conversion right now. It's going wonderfully. I strongly advise you to look into it, bet you'll find it way easier than you think.)
(One of the nicest things about it: we give every app its own cluster of two PG boxes, because you can just do that instead of running a centralised monster box with an expensive license. It turns out that just everything not having to play nice with others makes stuff stupendously easier to manage.)
This was all cobbled together following the docs. There are almost certainly better ways to do everything we've done so far.
The Postgres is just 9.3 out of the Ubuntu 14.04 repo. Oracle was STUPENDOUS overkill for what it was actually being used for, but MySQL wasn't up to the job.
The heavy lifting for the conversion is done using ora2pg http://ora2pg.darold.net/ Then there's a pile of faff and twiddling and unit tests and so forth. See also https://wiki.postgresql.org/wiki/Oracle_to_Postgres_Conversi...