If you are into making games, Monogame http://www.monogame.net/ http://www.monogame.net/ and Duality https://github.com/AdamsLair/duality https://github.com/Ada

If you are into making games, Monogame http://www.monogame.net/ http://www.monogame.net/ and Duality https://github.com/AdamsLair/duality https://github.com/AdamsLair/duality (very similar to Unity but 2d and OSS) are awesome open source projects to look at.