"Hackers, makers, artists, tinkerers, musicians, inventors—on any given day you’ll find them in The Microsoft Garage." So begins the blurb on what is effectively Microsoft's equivalent to the old Nokia Beta Labs, offering apps and games for free but evidently in an early state. Of note is that the Microsoft Garage titles range across different platforms, so it's not just Windows Phone, plus the apps all seem to be USA-only at the moment. 

From the official Microsoft blog post:

....It also represents Microsoft’s evolving culture, where experimentation is encouraged, failure is an option, apps are platform-agnostic and getting them to customers quickly for review is key to learning what will work and what won’t. The home base for this effort: The Garage, Microsoft’s haven for über geeks who are constantly thinking and tinkering. The Garage’s mantra is “Doers, not talkers.”

The Garage started out in 2009 in Office Labs with “a simple vision of giving people at Microsoft an opportunity to embrace their inner innovator and explore grassroots projects, mostly as side projects,” says Jeff Ramos, Manager of The Garage.

“Now the idea behind The Garage is to connect our engineers and engineering projects with real customers to evaluate how technologies are being received,” he says. “From a customer’s point of view, it’s a really great way to get first access to emerging technologies. And from Microsoft’s point of view, it’s really a great way to get real feedback from real customers on how people are using things.”

Apps like Mouse Without Borders, BusAlarm and Bing Keyword Distribution Graph flowed from the within the walls of The Garage on the Redmond campus. The Garage grew over the next five years into a global community of more than 10,000 hackers, coders and makers. The Garage evolved to support side projects and small-scale innovation from engineering teams across the company, giving customers early exposure to emerging technologies.....

...Microsoft Garage apps are reviewed first by an internal audience of Microsoft employees, with comments and suggestions back to developers on a daily basis before an app heads to a store.

Everything can be found in the Garage, though note that everything I looked up ended up 'not available' in the UK, and presumably anywhere outside the USA. Particular applications of note (that I'll try out when they get wider release) include:

• Tetra Lockscreen
  As the name implies, brings a four-fold set of functions in a single lockscreen: agenda, location, activity tracker and stopwatch
    
    
• Sound Stack
  A creative tool that generates melodies and chords based on tap and camera input 
    
    
• Collaborate
  A multi-user white-boarding tool
    
• Floatz
  An anonymous social network 
    
• Lost Turtle
  A retro arcade game