What is your favorite *general* and *free* language learning tool?

I know that some variant of this question has been asked a lot of times so far haha, but I am curious if anyone has any *general* and *free* language learning tool suggestions. I'm not talking about apps/websites to learn the language itself (like Mango Languages, etc)

I mean more like the dual subs Netflix/YouTube extension (Language Reactor), Forvo, etc

Something that has helped you on your language learning journey that isn't necessarily a grammar learning resource!