Anki really is a great tool.

Tip for people looking to use it: you can find premade decks (collections of flashcards) on various topics on the Anki website. For example, here are decks that are available under the 'Programming' topic: https://ankiweb.net/shared/decks/Programming

Not all of these decks are great, but there's a rating system, and this can sometimes be a helpful starting point for your own decks.