https://github.com/pkamb/PowerKey
I then sell a compiled version signed with my Apple Developer ID via Gumroad:
https://gumroad.com/l/powerkey
This model works pretty well for small apps that you otherwise want to keep in a public repo. The hassle of compiling + signing the app is worth $5 to many people.
For anyone dabbling with the idea, I can't recommend Gumroad enough for simplicity. But it would be nice to see payment/storefront functionality built into GitHub's Releases feature. A GitHub sanctioned payment system might even clue some creators in to the fact that you can charge for some component of your open source work.