It expands “Learn from your mistakes” to all your computer analyzed games and adds spaced repetition with the UI ported from lila so it feels like y̶o̶u̶’̶r̶e̶ b̶a̶t̶m̶a̶n̶ playing on Lichess. If you don’t play on Lichess, or don’t want to use your own account at first, there is a sample deck included so you can check it out.
There is also the option to use your own computer analysis to create cards from all of your Lichess games, not just the ones analyzed on Lichess’s servers. If you have lots of games, I recommend using your own computer to download the app so you have access to a better engine.
Other features included: suspending cards (positions) you don’t like, choosing if you want to focus on opening mistakes vs mistakes where your position collapsed, toggling your previous move arrow (this was a nitpicky one for me). Crucially, you can adjust how long a delay before you see a card again. I found somewhere between a 5 to 7 day delay was helpful to prevent just superficially recognizing a solution.
Similar tools that already exist include Aimchess and github.com/antimike/chess_trainer. I have the greatest respect for Lichess, and tried to build a tool that feels like a natural extension of their wonderful service.
Mistake Trainer is free, open source, and has no server to see your data (it stays on your computer). I hope you find it helpful in improving your chess!