Syntorial 2.0 (software for learning subtractive synthesis) is currently on sale

I realize this community isn't about product promotions, but I thought this one might be of general interest. Syntorial gives you a software synth and a very thorough series of lessons and challenges that teach you to relate the sound you hear or imagine to the knobs on your synthesizer. Each challenge gives you a sound which you have to recreate on the synth, and there are some quizzes too. It trains you to listen analytically and understand what you're hearing in a subtractive synth patch. I'm a user, not the maker of this software, but I have found it very helpful.