We all know that I don't have the willpower to learn languages, but… I'm currently in a "I'm totally learning Mandarin" phase, for like the 5th time probably, and I discovered one thing that is super helpful:
This tone training course! https://wordswing.com/cards/tone-training-course/
Actually, the whole Wordswing site is totally worth checking out, it's freemium but mostly free.
And for people who aren't beginners it's probably a lot of fun because there are text adventures designed specifically to learn Chinese? But I think at least one of them is paid. But still.