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Umlet allows that too. Though dragging won't change the structure.

https://www.umlet.com/

Nice list! How can I get https://cascade.page on there?

This is nice, added. At some point I will move the list to gist.github which will keep this page upto date.

You've clearly put a lot of work into assembling this list. I'm guessing the page would be significantly more valuable to readers and much more likely to be found by people interested in the the information in it if you added a brief sentence or two description of each of the projects.

More info I put there, more difficult it will be to keep it updated. There are tags/words below each to describe what that tool is for.

Wikipedia?

EDIT: https://en.wikipedia.org/wiki/List_of_Unified_Modeling_Langu...

This list is not a good fit for your XOSH list. It does include PlantUML but does not include a feature-breakdown. Instead it's simply a declaration of existence.