Introversion's slammer-sim Prison Architect has offered a playable alpha for purchasers through its official website for some time now, even racking up a cool million from buyers eager to yell at and bludgeon teeny convicts as a power-mad warden. The various purchase tiers are now on Steam , and it makes up a part of the first set of games offering immediate access to pre-release versions through Steam's new Early Access system.
All four of Introversion's alpha packages are part of Early Access, starting from the barebones $30 standard package to the $50 "Name in the Game" bundle that names an inmate after you and lets you supply his rap sheet.
The goal of Early Access is to bring gamers further into the development process itself, a trend that could help developers polish and broaden the appeal of their games while also providing some real-world compatibility testing and performance feedback.
Take a look at the Early Access page for more info and a list of the 12 games in the program so far including Arma 3, Prison Architect, and Kerbal Space Program.