Excalidraw is quickly becoming my main tool for illustrating quick concepts and creating wire frames.
it's super fast and lightweight. give it a spin. https://excalidraw.com . Its open source and you can just run it on localhost.

Ecosystem and product builder.

0xa5ad.twitter

And the Code extension is incredible. Name a file as .excalidraw or .excalidraw.svg and you have an excalidraw editor in vs code, that saves as an svg and works with git.

https://marketplace.visualstudio.com/items?itemName=pomdtr.excalidraw-editor