Microsoft has been open sourcing ton of projects recently and here is one more.
Millions of people rely on WorldWide Telescope (WWT) as their unified astronomical image and data environment for exploratory research, teaching, and public outreach. With OpenWWT, any individual or organization will be able to adapt and extend the functionality of WorldWide Telescope to meet any research or educational need. Extensions to the software will continuously enhance astronomical research, formal and informal learning, and public outreach.