Beerware

Beerware is a friendly way of saying "thank you" for using someone's software. The way it works is that if you use the free software, you can buy the person who made the software a beer as a way of thanking them. This gesture usually happens in person or by sending them a beer through the mail. This way, the person who made the software can get a reward for their work and it's a nice way of saying "thank you" for the free software they made.