I could, of course, name windows, which most of us are kind of beta testing
as the longest beta ever.
However, VGA Planets 4 if *officialy* in beta for 5 years now
Granted, given the quality of games nowadays, most companies would have slaped the gold sticker on this game more than 2 years ago, as there are only very minor bugs (IMO) and some balance issues left. But the game keeps getting tweaked again and again, mostly after requests, followed by a few weeks of discussion, from the community (which is a good thing IMO)
Ok, enough of planets and back to SoaSE
