Some project that might interest you:

• openage: github.com/SFTtech/openage, openage.dev, a free Age of Empires II engine clone
• stustapay: github.com/stustapay/stustapay - cashless event payment system
• abrechnung: github.com/SFTtech/abrechnung - payment splitting for groups
• stiefelsystem: github.com/SFTtech/stiefelsystem - boot your computer on another computer