Most, but not all, open-source apps are being welcomed by Microsoft into the Windows 8 Windows Store.
The Store’s App Developer Agreement (here) allows developers to build their apps for download and installation on Windows 8 machines using any open-source licence as long as it has been approved by the Open-Source Initiative (OSI).
The OSI is the body that monitors all open-source licences.
Microsoft’s agreement says:
“Your license terms must also not conflict with the Standard Application License Terms, in any way, except if you include FOSS, your license terms may conflict with the limitations set forth in Section 3 of those Terms, but only to the extent required by the FOSS that you use. 'FOSS' means any software licensed under an Open Source Initiative Approved License.”
The invitation does not extend to GPL.
Microsoft’s agreement continues:
“If your app includes FOSS, it must not cause any non-FOSS Microsoft software to become subject to the terms of any FOSS license.” Although Microsoft didn't name it, it's talking about GPL.
Microsoft has been warming to open-source apps for years now, as a way to help sell more copies of the underlying Windows client and server operating system.
The company has been working with many different open-source projects to tune them for Windows; Microsoft, though, has assiduously avoided actually shipping open-source software with its own products, in case this left it open up some kind of legal or IP liability.
Now, though, it seems Microsoft is getting over this – at least in regards to the vast majority of open-source licences that are considered “business friendly”. GPL remains out in the cold. ®