I like Rubik's puzzles and similar. I'm OK with a 3x3x3 but usually need to look up permutations on the rest of them. Here are some of my favorite guides.
Didn't you used to develop web? Why this site look so bad? Because developing web is a fool's game. I'm a fine programmer, but to hell with web programming. It makes you crazy. Basic HTML with no CSS is perfectly responsive and looks just as bad on a phone as in a browser. So there.