chruby: ultra-minimal ruby switcher
chruby is an ultra-minimal alternative to RVM and rbenv. chruby allows one to install rubies into
~/.rubies/$ruby, but install gems into
~/.gem/$ruby/$version. Unlike RVM or rbenv, chruby only modifies
$GEM_PATH, and does not hook
cd or rely on shims. chruby is ~80 lines, supports both bash and zsh, and has unit-tests.