Neat idea! I mostly like them for languages (spoken, not programming) but I can see it being great for programming languages too. I guess there are loads of topics that could fit into this.
Do you envision that your site will enforce a particular layout(s) and style for the cheatsheets? Or will it just be more of a catalogue?
Enforcing a style/layouts is an interesting idea. Having that kind of consistency could be a good thing. Maybe having composable templates and a style guide would work.
I was thinking that it could be a catalogue with broad categories that would allow people to surf through for cheat sheets they might want to read, but there would also be room for more esoteric subjects.
Also, it'd be cool if it could be a platform where people can sell their cheat sheets. People could post free ones, too, and would be encouraged to do so because it'd be made easy for them to make an awesome infographic-y cheat sheet, but being able to make some money would incentivize quality too.
Curious, do you mean for just languages, or in general?
I was recently thinking that a site with user-uploaded cheat sheets for all sorts of subjects would be pretty rad.