Non-Linux FOSS: Snk
I'm apparently in a silly-game mood this month, because I stumbled across an open-source project I couldn't keep all to myself: Snk. If you remember the classic game of snake, Snk is the same concept, but smaller, harder and with music.
I actually really like the Snk program because it's fairly simple, and the developer (Mowglii) has put the Xcode project on GitHub for folks to download. If you're just starting with OS X Swift development, Snk is a project you can tweak for some learning on the fly.
My favorite part of the project is actually the "reviews" for it. Head over to http://www.mowglii.com/snk to grab Snk and its source code today. And, good luck with level three; I run directly into the wall every time!