Describe a useful website or app

The app I find most useful on a daily basis is one called Anki — a flashcard programme that uses a spaced-repetition algorithm to decide when to show you each card again. I've been using it for about three years, primarily for language learning but also for remembering professional terminology. I use it for maybe twenty minutes a day, usually in the morning before anything else. What makes it genuinely useful, as opposed to just another study tool, is the underlying algorithm. The idea is that reviewing something at the exact moment you're about to forget it is more efficient than reviewing it on a fixed schedule. So items you know well appear less frequently; things you keep getting wrong appear more often. Over time, it means you're spending your study time only where it's actually needed. The reason I keep coming back to it, though, isn't really the algorithm — it's the habit structure it creates. Because the daily review only takes a fixed amount of time once your deck is established, it feels manageable even when other things are busy. I've maintained a consistent streak of over six hundred days at this point, which I don't say to brag but rather because I find it genuinely surprising — consistency has never been my strong point. The one downside is that it requires you to create the cards yourself, which takes time upfront. But I've found the act of making cards itself reinforces the material, so it's not entirely wasted effort.