virtualenv solves virtual environment as much as pip solves OS package management. Not that it's not useful, but you see all over where you have little fiefdoms that work pretty well for their little ecosystem, but become a mess if you integrate stuff outside (virtualenv, rbenv or pip, npm, gem, rpm, apt or make, ant, scons, jam).
A lot of these systems are just reimplementations tailored to language-X. Nix is pretty unique and clever. For example, you can effectively version control you virtual environment, it's at the OS level, and accommodates major languages and libraries (Python, Perl, Lua, Java, Go, Qt).
A lot of these systems are just reimplementations tailored to language-X. Nix is pretty unique and clever. For example, you can effectively version control you virtual environment, it's at the OS level, and accommodates major languages and libraries (Python, Perl, Lua, Java, Go, Qt).