With Owlbear Rodeo 2.0 getting officially released the developers haven’t quite made made good on their promises to open source the original Owlbear Rodeo (releasing under a non-commercial license instead of a proper Open Source license what they are now calling “Owlbear Rodeo Legacy”), but the source is available on GitHub, complete with a docker-compose file to spin up your own instance.
The post originally called it open source, OP changed it.