Ravaged, Chivalry, Airmech, Guns of Icarus, Gear Up, and several others have had betas on steam (DOTA2 and CS:GO, if you want to count them). They generally have only been accessible by using a key from the developers, and have always been clearly marked as beta.
The Towns developers have said that the game is
fully playable and enjoyable, but many in the community disagree that that means it is ready for release.
Personally, I've had a lot of fun with it, but I think the devs have done themselves a disservice by releasing it in its current state. Maybe they couldn't wait for monetary reasons. Who knows?