I'm not sure whether it's an improvement over UML for your use case, but I've really grown to like Graphviz for things like that. I really like it that I don't actually have to draw anything, I can just type foo -> bar into a text file and that's it.

I prefer documenting software right alongside code so that it's easier to keep them in sync. My current workflow is to use markdown paired custom renderers like mermaid-js for diagrams. https://mermaid-js.github.io/mermaid/#/ It covers most of the usual diagrams.

There's also PlantUML that integrates with Lein: https://github.com/vbauer/lein-plantuml and several editors e.g. IntelliJ IDEA, Eclipse, VSCode, Emacs etc. PlantUML is text-based UML, and relatively easier to keep with the source code.

pen and paper ?

http://draw.io is a great tool, I agree 🙂

Not quite the same, but just last week I arrived to the (common) epiphany that I should start learning how to really use google sheets (data validation, automatising data input) because it’s the fastest way to get non-technical people at my company to give me sane data

They already use sheets, and so far I’ve build tools for them as clojurescript web apps. I think I would have saved myself a lot of time had I done it on sheets instead

I had to take over a website that used Google spreadsheet as the backoffice. It worked for simple stuff. It broke horribly once you got complex data that you need to handle

I’m definitely thinking about simple stuff. Maybe 6-7 columns total, no crazy joints or anything.