2
RC stands for Release Candidate, which is like a public beta release. This release isn't meant for live websites, but for the community to test, find and report bugs, and for developers and designers to see how it works.
XOOPS 2.0.5.2 isn't a Release Candidate but a stable version fit for a production environment. About a year ago, a few XOOPS2 Release Candidates were released, and some developers and designers made modules and themes for that. But, when XOOPS2 Final was released, som ethings had changed, rendering those modules and themes unusable. That's the risk of working with Release Candidates. And since then, the XOOPS Team has become careful with releasing big changes like that.
Herko