MoneroTipper
The project was started in the summer of 2019 and has since made 9 major releases and been hosted on moneroecosystem.org. With over 200 users signed up to the service, it is the first project of its type, and is a one in a thousand project that actually uses a blockchain for a legitimate purpose.
See the source code here: https://github.com/monero-ecosystem/MoneroTipper