Some years ago, I ended up on a call with a support team guy, helping him under some parts of a system I worked on. He shared his screen, started drawing diagrams. It took me a whole 10 minutes to realise it was in paint, he was just that good at using it.

Turns out paint was the thing almost every customer had installed/had access to, so he worked to the lowest common denominator and got really good at using it. I guess now he'll need to find a new tool to astonish devs with.