Gentoo’s Portage and NixOS’ Nix are both interesting takes on package management. Both are powerful and open up a ton of flexbility to the user, but still do a lot of work for you.
Are there any other similarly interesting approaches to the package management problem?
Guix is another one. https://guix.gnu.org/
Is guix much different from Nix? I remember that it uses scheme instead of nix language, that it is more free-software purist, and also has less packages than nix. Are there any benefits?
Guix re-implemented the Nix package manager on Guile, so yes, though similar in principle, they are different, and if you go beyond the package manager, to the Guix system vs NixOS the differences are even bigger. So it’s more than OK to mention them separately.