[brucou]

If we talk about professional use, then Powerpoint (many years ago), then Visio (also many years ago), then yEd (by yWorks, https://www.yworks.com/products/yed). Then there are a ton of specialized open-source tools, with varying quality. Mermaid improved a lot. PlantUML has a lot of options, but I would not use it professionally. draw.io has also plenty of options, but has some usability issues in the frame of a frequent, professional use.

For anything UML-related, Enterprise Architect is quite good, but boy you better know UML. That ain't user-friendly in the least. But super powerful and there are a few more like that out there with somewhat limited free versions.

Long story short, my best choice is yEd. And I still reach out to Powerpoint every now and then.