Package managers are way more modern than that and their design does by itself not require root (see pip). You can in fact run most package managers without root, you just won't be able to modify system files. You can use them to install a chroot as regular user, e.g. `zypper --installroot ~/tw install bash`.

FUSE doesn't really relate to single vs. multi-user AFAICT.

Users are perfectly sandboxed if you configure the system that way. Depending on the distribution that's even the default.