[egorr]

I like C4 for system design overview and sequence diagrams to show detailed process of interactions in one particular scenario. I found these two the most useful for me.

I also like to write diagrams as code with https://plantuml.com/sequence-diagram cause you can then add it to git and easily version it. Also, a lot of tools on the market have support for PlantUML

[Graziano_M]

swimlanes.io and Mermaid (https://mermaid-js.github.io/mermaid-live-editor/edit) are other 'diagrams as code' options.