Microsoft Shared Source License(s)
Yes, Microsoft have their own open source licenses, and is named Shared Source Licenses. There are actually three levels of license, depending over how licensee (the user of the source code) can act over the source code. The licenses are Microsoft Reference License (Ms-RL), Microsoft Community License (Ms-CL), and Microsoft Permissive License (Ms-PL).
Basics: every type grants the licensee the right to use the code. The right to use the code is non-exclusive (means that not only you get the license), worldwide (means everyone, including those embargo-ed by USA), and royalty-free (means you don't have to pay for it).
Ms-RL: is the most restrictive. You can read the code, use it for internal use, but you CANNOT distribute it to anyone not in your company (non-transferable). Period. In addition, the license covers Windows-only solution. Mono and ROTOR does not count.
Ms-PL: is the least restrictive. You can read, redistribute, create derivatives, and distribute that derivatives without limitation. There's a limited version, which covers Windows-only solution.
Ms-CL: is the balanced license. The license granted is just like Ms-PL, BUT if you redistribute software that uses the original code, the original code should be licensed as Ms-CL, nothing else. There's also a limited version.
Here's a quick summary:
License | Ms-RL | Ms-CL | Ms-PL |
Transferable? | No | Yes | Yes |
Changeable? | No | Yes | Yes |
Redistributeable? | No | (only with the same license) | Yes (unlimited) |
Windows-only? | Yes | No, but Yes with Ms-LCL. | No, but Yes with Ms-LPL. |
I imagine there be a lot of activities on Ms-CL. Even I'm starting a new pet project using Ms-CL license. Ms-CL provides guarantee that your works will never be re-licensed using other license (such as Ms-PL, Ms-RL, or closed-source) but encourages contribution by opening up the source code to the public.