A topic close to my heart! One thing though, lots of these tools are "offline", but some are found here as a repackaged service online. Personally, if I'm diagramming some important things, I don't want to trust yet another third party, and largely prefer "offline" tools, and I suspect there are others that have the same view. For testing the tools this is great though.
Blockdiag [3] is the one I tend to use the most, with both Mermaid [2] and the unoriginally named "diagrams" [1] being the two others I find the most interesting.
1. https://pypi.org/project/diagrams/