draw.io -- [browser based](https://www.draw.io/ https://www.draw.io/) as well as [desktop drawing tool](https://github.com/jgraph/drawio-desktop/releases/tag/v

draw.io -- [browser based](https://www.draw.io/ https://www.draw.io/) as well as [desktop drawing tool](https://github.com/jgraph/drawio-desktop/releases/tag/v12.9.9 https://github.com/jgraph/drawio-desktop/releases/tag/v12.9....) with many templates for flowcharts, UML, etc. Free and very useful.