> while studying I do pretty regularly think, "man, this would be so much better if it did X; I wish I had an app to do Y", etc., etc.

This is more or less exactly why, despite having played with a lot of different tools, I always come back to Anki. The UI is irritatingly unpolished, and it's difficult to learn well, but it's also the only tool out there that's open and flexible enough that I can easily experiment with and tweak what I'm doing without disrupting my overall learning process overmuch.

I've certainly nerdsniped myself a few times, especially when I'm trying to build something from the ground up because I'm currently toying with some other app. With Anki, though, most of my "app to do Y" ends up just being a Jupyter notebook that I hacked together in less than an hour.