Mars Colonies - A free old-school RTS... on Mars
Google Open Source - All of Googles open source projects under a single umbrella
NASA App - Showcases a huge collection of the latest NASA content
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
UX Timeline - See how some of today's best companies have evolved
Open Source @IFTTT - A collection of IFTTT OSS projects.