Isolate is a tool for managing RubyGems by including them within the project that requires them. Authors sees Isolate as a stable, very simple, and scalable project. Most importantly, new developments and feature enhancements have been welcomed with open arms.

To get started you have to install Isolate gem. The usual gem install isolate will do the trick just fine. Once you have Isolate installed, you must initialize it in your project. The you can put initialization code info config/preinitializer.rb file. In non-Rails projects, put the following in the file that’s loaded first, or a file that’s loaded before any gems are required.

require 'rubygems'
require 'isolate/now'

That’s all that’s required for Isolate to be initialized. Isolate will now look for a file called Isolate in the current working directory. The Isolate file contains lines that describe which gems are to be installed for your application. Here’s a sample Isolate file that specifies some gem dependencies

gem 'chronic'
gem 'mysql', '2.7', :args => '--with-mysql-config=/opt/local/bin/mysql_config5'
gem 'mime-types', '1.15', :require => 'mime/types'

When Isolate runs (in the app’s initialization), it will install the latest version the chronic gem in your application.

source: http://stevenrbaker.com/blog/2010/06/01/introducing-isolate.html