The version that everyone uses is 2.2RCa (release candidate A). They're currently trying to have a final release of 2.3 but it's a bit of a mess right now as it incorporates some needed bug fixes and security measures, and then adds a lot of unnecessary changes that will break many of the most popular add-ons. Version 3.0 is still a dream basically. Most of the osC veterans on their forum will tell you not to use 3.0 yet, and that's been the case for multiple years now.