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 the problem, I've demonstrated it 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.
Anyone up for the challenge of creating that type of app, or perhaps something like this already exists? Let me know!