Microsoft is adding another cross-platform application-development vendor to its stable in order to try to get more applications built for Windows 8 and Windows Phone 8.

The newest partner is Corona Labs, which makes a software development kit for building 2D apps across platforms. Corona claims it has 300,000 developers worldwide using its SDK to publish apps to iOS, Android, Kindle and Nook devices with a single code base.

Corona's SDK will support Windows Phone 8 in the first quarter of 2014, with Windows 8 support coming some time after that, Corona officials said on October 29.

Microsoft has forged deals with a number of other middleware partners -- including Unity, Marmalade and Havok -- to provide cross-platform frameworks for porting games and apps to its Windows platforms.

Game developers are a big part of Corona's target audience. Corona officials told me about 70 percent of their SDK users are building games, with the other 30 percent building business apps, utilities and e-books. Games make up about one-third of all Windows Phone downloads and roughly 60 percent of revenue, I've heard from various sources.

"Tens of thousands of developers are using Corona SDK to build 2D/2.5D games and apps, including business apps, utilities and ebooks," said Corona Labs' Chief Operating Officer David Rangel. "This is a fairly different set of developers from those using something like Unity, which is a great tool for 3D games. Developers choose Corona SDK because they can build 2D games and apps much more quickly and easily than in tools that were originally built for other purposes and/or platforms."

Rangel said that developers who've built apps for non-Microsoft platforms using Corona's SDK will be able to reuse 95 percent of their code in building their Windows Phone and Windows 8 apps. While there isn't (yet) a unified Windows Phone 8/Windows 8 app store, Rangel said code reuse between Microsoft's two mobile operating systems "will be very close to 100 percent" for those using the Corona SDK.

There are currently about 175,000 apps in the Windows Phone app store, and more than 100,000 Metro-Style/Windows Store apps in the Windows 8/8.1 Store. Microsoft recently began packaging up some popular Web sites in app form for Windows Phone -- a move which earned the ire of some of the site owners.