A massive list of single line commands (sometimes a bit convoluted, but still) with a simple explanation of what it does.
I wouldn't use this as a lookup to "do a thing" but it's extremely useful to browse and see what's possible and how you can go about it.
The list is based on linux so for Mac users (like me) won't be able to run every command, but they're still super useful for learning.
Source: linuxcommandlibrary.com