1. Gymnastic rings - cheap, so simple yet so complicated. Magic ancient alien technology from the future (whatever that means)
2. Anki - free, you remember what you want to remember, but you have to RTFM to use it properly.
3. Wax earplugs - cheap. My sleep quality is at least 2x better since using them.
4. Org-mode - free.
I’ve been tempted to get a set of gymnastic rings for a while. For someone like me who tries not to accumulate too much junk, buying any kind of bulky gym equipment is not an option.
Gymnastic rings seem like the perfect minimalist’s exercise equipment… the only thing is I have no idea where I would hang them.
Info dump alert, Anki is a deep deep rabbit hole. These resources have helped me immensely. I didn't have any specific hurdles in mind - I had many "eureka" moments, but they were highly personal, only applicable to my situation. In the words of Michael Nielsen "Anki use is best thought of as a virtuoso skill, to be developed", so don't get discouraged by this big list, take one step at a time. If I had to give only one recommendation then the top link would be it.