A Desktop App Idea That You Can Develop and Even Sell
From hn - I guess the op won't mind ;)
I often hear people saying they don't know what to build, so here's a desktop application idea that solves a real problem for people who create screencast style videos.
Rather than explain it, I've demonstrated the problem on video (~3min):
The TL;DR is when your desktop resolution > recording resolution you lose a lot of common Windows functionality and have to manually pixel align windows inside of recording tool constraints. I'm sure there's Windows APIs and methods to restrict windows operations to a customized rectangle, and that's the app you could potentially build.