It's GPL, but I plan to change it to LGPL once I declare it stable and documented enough.
https://gitlab.com/dosowisko.net/libsuperderpy/
Games live here: https://dos.itch.io/ (or more specifically, https://itch.io/c/195242/libsuperderpy-engine). Most are small game jam things, but recently I've been working on bigger ones as well.