rbenv-gemset is an extension for the rbenv ruby version manager that allows you to use "gemsets", sandboxed collections of gems. This lets you have multiple collections of gems installed in different sandboxes, and specify (on a per-application basis) which sets of gems should be used.
The easiest way to install (if you are on Mac OSX) is via the Homebrew package manager:
$ brew update
$ brew install rbenv-gemset
Otherwise, clone rbenv-gemset to the $HOME/.rbenv/plugins directory:
$ mkdir -p ~/.rbenv/plugins
$ cd ~/.rbenv/plugins
$ git clone git://github.com/jamis/rbenv-gemset.git
In your application directory, create a file named .rbenv-gemsets and put the
names of the gemsets you want to use in it, separated by whitespace. The first
gemset in the list will be the primary gemset, where new gems will be
installed.
$ echo my-gemset > .rbenv-gemsets
Now, all commands involving gems will use the gemsets you specified.
The gemset plugin will cause rbenv to search for the .rbenv-gemsets file in
the current directory, as well as in all ancestor directories, so as long
as there is an .rbenv-gemsets file at or above the current directory.
Alternatively, you can set the RBENV_GEMSET_FILE environment variable to the absolute path of the gemset file.
This code is placed in the public domain by the author, Jamis Buck. Use it as you wish. Please prefer good over evil.