K2 Cube drills the algorithms speedcubers use for the last layer: two-look OLL and PLL for beginners, full OLL (57 cases) and PLL (21 cases), ZBLL, and Roux CMLL (two-look and all 42 cases).
Every algorithm in the sets is machine-checked to solve its case, and the cases you hesitate on come back until recognising them is instant.
Every card has a temperature. Get it right and its chance of coming back halves; miss it and it doubles. K2 picks the next card at random, weighted by that chance, so a session keeps returning to whatever you are getting wrong and lets what you know fade into the background.
When the cards you are working on have cooled, a new batch joins them, so you always study at the edge of what you know. There are no review dates and no daily queue to fall behind on. Every drill is free and works without an account, and everyone gets 20 free AI uses a day; past them, signed-in AI practice runs on your Bike4Mind credits.