There is Wick Editor (which I mentioned elsethread)

https://www.wickeditor.com/#/

Unfortunately, it's been abandoned for a while now.

There are some forks of it that seem more recent:

1. Candlestick https://github.com/Candlestickers/Candlestick

2. StickmanRed’s Fork https://github.com/StickmanRed/wick-editor

3. This brand new fork: https://forum.wickeditor.com/t/started-my-own-fork-luke-tool...

That is unfortunate.

Other similar projects?

Another reason for me to knuckle down and write my own (programmable) drawing program....