How do I share my flakes for external projects?

Every now and then I see a program that doesn't have a default.nix or flake.nix in the source, doesn't have an entry in nixpkgs, and otherwise can't find a derivation for. So I write them myself.

What's the best way to share these? Should I contribute to nixpkgs? (does this count if I'm making flakes?) Do I maintain a single repo for each program? Or do I create a repo with a collection of flakes? Something else?