In 2009, Markus "Notch" Persson released Minecraft. Sort of. The revolutionary construction game wasn't anywhere close to done, full of bugs and missing most of its planned feature set. But by paying Persson a few bucks, players could start messing around with Minecraft while it was still in development. The model proved a tremendous success -- Minecraft had so many players and had made so many millions that by 2011, the game's "official release" passed almost without notice. Developer Mojang had been able to leverage the funding and feedback from pioneering players to turn Minecraft into something different, maybe better, than it would have been had Mojang labored away in secret, the traditional way. It's clear why other game developers might also want to try out the pay-for-early-access model. They can address bugs and fundamental design flaws thanks to feedback from early-access players while simultaneously making enough money from sales of the game to sustain themselves during its development. And some of them are learning lessons they'd never have stumbled upon without a massive group of engaged players banging away on the in-development versions. We've selected and explored a handful of the games that are embracing this new model, both from big-name developers like Valve (Half-Life) and one-man indies like Jason Rohrer (Diamond Trust of London). Above: The Castle Doctrine For the past few months, Jason Rohrer has struggled to deal with the clever players of his massively multiplayer home invasion game, The Castle Doctrine, for $8 on PC, Mac and Linux. The game was originally about building houses full of traps, which other players would attempt to successfully sneak through. Players are given access to tools to disarm traps and sneak through walls, and can use them to burglarize the homes of any other player in the world. Soon after Rohrer began selling access to players for the alpha version of the game, those players broke it. In their attempts to design impenetrable fortresses, some players discovered exploits and began to design their houses as incredibly complex puzzles. One particularly bright player discovered how to make a 16-button combination lock system by using a combination of wiring and Boolean button logic. Soon, all homes were protected by 16-button lock systems, and then 22-button lock systems. "This was essentially overkill," Rohrer wrote on his blog, "because the 16-button one was unbreakable... if you don't know the secret pattern, it might take you 65,536 guesses." The Castle Doctrine was no longer a game about home invasion. It became a locksmithing simulator. "Some of the resulting houses literally required expertise in electrical engineering to solve and successfully rob," Rohrer tells Wired. "I took a step back and realized that I never wanted to make a puzzle game, but that's where the game was going." Rohrer's solution was throw all that in the trash. In the newest version of The Castle Doctrine, Rohrer changed the prices on in-game items, he's created scarcity in the game. As the game's designer and ruler, he's changing it back into what he always wanted it to be. Now that's defending your castle.

SpyParty SpyParty creator Chris Hecker has been showing off the game regularly to the public since 2009, but only recently has he opened up the game for a $15 public beta for Windows machines. Hecker's two-player game pits a spy against a sniper who has only one bullet in his clip. The player controlling the sniper has to identify and eliminate the spy before he successfully completes a short checklist of goals. Speaking to Wired earlier this week, Hecker touted the values of paid betas, saying "The nice thing about a paid beta is it doesn’t trigger my perfectionism warning signals. My brain will let me do a paid beta, but it wouldn’t let me ship the game early."

Scrolls Mojang's first non-Minecraft software release is… a collectible card game? Scrolls is part Hero Academy, part CCG. If you've ever played a card game that involved magic and/or gatherings, you'll probably feel pretty comfortable with Scrolls' conventions. The $20.95 PC and Mac game's rules page details some of the complexities of each collectible scroll (read: card): health, resource costs, extra traits, special rules. It's no wonder Scrolls has taken this long to reach a playable state when it's this complex.

Kerbal Space Program Despite its cartoonish mascots, Kerbal Space Program is a deep and fully-featured space program simulator for PC, Mac and Linux. Kerbal rep Miguel Piña explains: "You may design a behemoth of a ship that is so heavy and powerful it simply collapses on the launchpad in a brilliant display of fireworks, or a slick and optimized rocket that safely gets your crew to other worlds and then back home." Kerbal's green mascots are expressive in a Looney Tunes sort of way, so when your shuttle launches go bad in historically-reminiscent kinds of ways, it doesn't seem quite as somber. The game was originally funded entirely by donations, but has been in paid alpha since April 2012, and now costs $23. Only 11 people currently work on the game, but Kerbal developer SQUAD reports that over 43,000 people play the game on average every day.

Dota 2 Valve's sequel-to-a-mod-of-a-Blizzard-game Dota 2 will eventually be free-to-play, but Valve has been charging for access to a beta version since 2011, and over 3.5 million players have paid at least $9.99 for the privilege of getting early access to this Windows game. The game pits two teams of heroes—characters with specific abilities, selected from a massive character roster—against one another in a relentless battle that can sometimes last for hours. The game is Valve's answer to Riot Games' League of Legends, which the company says averages about 12 million unique players daily.

Wildfire Worlds Pitched as a cutesy, papercraft alternative to SimCity, Wildfire Worlds is a beautiful and very weird simulation of city life for PCs and Macs. Unlike SimCity, the game isn't about building up a functioning society—it's about tearing down a perfectly good one with riots and destruction. Developers Dot Product pitch the game by saying "Did you watch the London riots on the TV, and think 'I want to play that?' If so, then Wildfire is just the thing for you!" The game is available now in an alpha state for $15, and is currently on Steam Greenlight.