Mermaid Chart makes it super easy for me to create diagrams and flows to use in my day to day workflow or for visualising ideas and mapping out processes quickly - it's helped me enable developers better and facilitate better communication between product & engineering!
An amazingly good and simple product. I use it all the time at work to create Sequence Diagrams to align with customers and internally with the tech team.
It's like writing pseudo code but with the added benefit of it creating visuals for you. Big fan!
I've found Mermaid to be a great tool for putting diagrams into GitHub - it only takes a few minutes to learn the syntax and the docs are really clear.