Also OmniGraphSketcher, a wonderful and unique utility that Omni divested from. Kindly, they open-sourced it;[0] sadly, the project shows no activity since last year and would seem to be abandoned.[1]

[0] https://www.omnigroup.com/blog/setting-omnigraphsketcher-fre...

[1] https://github.com/graphsketcher/GraphSketcher