We've forked excalidraw a while ago to allow running excalidraw without firebase as a backend. This can already be self-hosted. It needs some love, but it's a good starting point:

  * https://github.com/b310-digital/excalidraw
  * https://github.com/b310-digital/excalidraw-room/
  * https://gitlab.com/kiliandeca/excalidraw-fork
  * https://gitlab.com/kiliandeca/excalidraw-storage-backend