This is kind of obvious, but I cannot imagine what I would have done without my dictionary on my phone. Wherever I am, I can check any word I see or hear, it’s really one the most helpful tools you can have. My dictionary’s called JED, on Android.
Recently I decided to learn how to read Korean (because why not?) and so I needed explanations on how it works, and what better way to optimize language learning than by being taught in a language you’re already studying! Killing two birds with one stone as they say.