[chriswarbo]

> or the most part, Nix can install multiple versions of a program but only one can be in use at any given time.

That's a bit hand-wavey. More precisely: when you run a command, like `python3`, you can only associate that with one file. If you want multiple Python 3 interpreters, you'll have to use different names (e.g. making symlinks).

Alternatively, you don't need to bother "installing" anything; e.g. I use Nix for projects which use Scala, Maven, Python, NodeJS, etc. yet I don't have any of those installed. Instead, each project includes a `shell.nix` file which specifies the tools it wants. Running `nix-shell` in different folders gives me access to different tools.

Also, with Nix we only need to care about the end result: we can "install" a bunch of different programs, even if they have incompatible dependencies, since we're not "installing" those dependencies. ("Install" just means putting a symlink in some bin/ folder, like /run/current-system/sw/bin on NixOS or $HOME/.nix-profile/bin on non-NixOS)