and many more but this is still not the entire list:

https://github.com/Xamarin

https://github.com/PowerBI

https://github.com/MicrosoftEdge

https://github.com/yammer

https://github.com/OneDrive

https://github.com/MicrosoftResearch

https://github.com/LIS

https://github.com/DynamicsCRM

https://github.com/MicrosoftDX

https://github.com/ms-iot

https://github.com/microsoft-mobile

https://github.com/thaliproject

https://github.com/OneGet

.

Please take a look here: https://microsoft.github.io