Draw.io is nice!
It's a program that make nice diagrams and so many other things.
Works OK in a browser, on desktops and it's cross platform.
Running it locally
There's a handy docker image at fjudith/draw.io that I started using.
I made my homelab network diagram with it, then exported a png image from it.
A command like this can run it locally, as non-root with user:
docker run --user 1234:1234 --rm -d --name=draw -p 8080:8080 fjudith/draw.io:alpine
Here's my first diagram
This is the first diagram I've made with it:
More details on this image can be found in this post: