Microsoft's Windows Store -- the built-in app store for Windows 8 and Windows RT -- is open to all developers in 120 markets, as of September 11.
Of these 120 markets, 82 are newly supported, as of today, according to a new post on the "Windows Store for Developers" blog. (Here's a list of the markets now supported.)
To reward developers "for their interest and commitment to Windows," Microsoft officials have said they are providing all eligible Microsoft Developer Network (MSDN) subscribers with a free, one-year Windows Store developer account as part of their MSDN benefits. ("Eligible subscriptions include Visual Studio Professional, Test Professional, Premium, Ultimate, and BizSpark," according to the Softies.) Microsoft's DreamSpark program for students also waives the Microsoft Store subscription fee.
Here's Microsoft page listing available Windows Store app-development tools and resources, including Visual Studio 2012, the Windows 8 software development kit, certification kit for Windows RT, samples and more.
As of early August 2012, there were an estimated 450 or so WinRT-based, "Metro-Style" apps in the Windows Store. More recently, I've seen estimates of anywhere between close to 800 and 1,000 (depending on whether international versions of certain apps were counted). Directions on Microsoft analyst Wes Miller says there are 1,033 Windows Store apps available internationally as of today. Directions has a good report on "State of the Store" with further breakdowns on available Windows 8 and Windows RT apps.
The vast majority of apps already in the Store are games and other consumer-focused offerings, which isn't too surprising, given Microsoft is targeting Windows 8 at consumers more than businesses right out of the gate. Microsoft has been looking to recruit developers of all stripes via workshops, bootcamps and proof-of-concept development programs for the past few months. The company is holding its second Build developers conference in late October, when it is expected to provide more details and guidance to developers about how to write apps for Windows 8.
Windows 8 and Windows RT will be launched on October 25. The new operating systems and Microsoft's Surface RT tablets will be available on October 26