rbenv

Check latest Ruby version available: https://github.com/rbenv/ruby-build/tree/master/share/ruby-build
Update to get access to new Ruby versions: brew update && brew upgrade ruby-build
List all installed: rbenv versions
List all available to install: rbenv install --list-all
Install: rbenv install X.X.X
Set global default: rbenv global X.X.X
Set version for a project: add a .ruby-version file containing the version number