[squimmy]

You're more than welcome to make one yourself.

It could even just be a github repository.

Edit: I don't mean to sound accusatory, but it is much more likely to actually happen if someone takes the first step.

[Razengan]

Alas, I feel the need for such a thing precisely because I only have ideas and lack the will to implement them. :(

I specified game design because I think it would benefit the most from such an "ideawiki"; there's still lots of untapped genres or cool things from 20+ year old games that haven't been reintroduced in a modern way, but really there must be all sorts of apps that people have ideas for but are unable to make themselves,