Hi! I struggle with deciding what problems to solve. For this reason, part of my practice routine has been looking at the problems that user X has solved and trying the ones I haven't solved yet. Obviously keeping track of which problems I had already solved before opening them became impossible, so I made a small web app called Upshift to do this automatically. You can try it here: https://upshift.upshift-practice.workers.dev/

The idea is simple: you enter your Codeforces handle and other handles you want to learn from. Upshift then builds a problemset containing the problems they have solved but you haven't. From there you can search and filter the problems by rating, tags and change the ordering. There is also a random problem picker where you can specify a rating range. Everything is stored locally in your browser, so there is no account or login needed.

The project is open source here: https://github.com/donaldgera/upshift

I built it for my own practice, but I thought it could also be useful to other people :)