I use PlantUML[1] for my UML diagrams. - It uses a human readable text-based file format renderable via the PlantUML jar. Friendly to CLI and git. - The diagrams are stylable, should you wish to style them. - There's a PlantUML Integration IntelliJ plugin that's easy to use for preview/rendering[2] - Overall simple to use, but I imagine it can as robust as you want it to be. For example, the IntelliJ plugin Sketch.it…
plantuml is nice one. Works smoothly with VSCode extension.
And wow, mermaid has gantt chart !