https://mermaid.live/ ! Mostly because it lets me generate my diagrams in code rather than drawing them out by hand, which means I can version control them, as well as generate said code from human-language descriptions given to ChatGPT. Sequence diagrams are an especially favorite of mine.
There are a few good options in the code to SVG (PNG, JPG, whatever) space besides Mermaid. The venerable graphviz has been around since the 90s, I think, and uses the DOT language. The newer D2 language probably has the nicest overall aesthetics as well: https://play.d2lang.com/
Thanks for posting this. I can not t use Graphviz as the diagrams look too amateurish to be shared in a presentation . But D2 diagrams look amazing and polished. I will try it out and maybe I can finally get rid of Visio. I find working with Visio very tedious.
There are a few good options in the code to SVG (PNG, JPG, whatever) space besides Mermaid. The venerable graphviz has been around since the 90s, I think, and uses the DOT language. The newer D2 language probably has the nicest overall aesthetics as well: https://play.d2lang.com/