For diagrams, have you tried PlantUML [0]? I've just recently been trying it out and found it very easy to work with. Being able to compose diagrams with text is so powerful IMO (and excellent for collaboration). Definitely take a look if you haven't already. There are plugins for most IDEs as well so you can live-edit your diagrams. It's open source too which is a huge plus (if not a requirement altogether).

[0] https://plantuml.com/