You can Nixify appimages pretty easily. Oh, and you can run flatpak with a single line of config and install things that way. Oh and you can build from source using the language's package manager (e.g. cabal install etc). I've even just run the Windows exe using Wine (super easy with Nix - it has great Wine support).

Obviously the ideal is built from source. This has a lot of benefits. It allows you to overlay the package very easily - modify its source to be a fork, change compile options, etc. It allows you to expose its dependencies. Stuff like that.