RubyGems is a package manager for the Ruby programming language that provides a standard format for distributing Ruby programs and libraries (in a self-contained format called "gems"), a tool to easily manage the installation of gems, and a server for distributing them. A package management system is a collection of tools to automate the process of installing, upgrading, configuring, and removing software packages from a computer. ... Ruby is a reflective, object-oriented programming language. ...
Ruby on Rails, often called RoR or just Rails, is an open source web application framework written in Ruby that closely follows the Model-View-Controller (MVC) architecture. ...
External links
Official Rubygems documentation
Official Rubygems project page, including downloads
RubyGems is a packaging system for Ruby applications and libraries (similar to CPAN for Perl).
Rubygems will be included in Ruby’s standard library in Ruby 1.8.4, and chances are high that it will become the de-facto standard for Ruby packaging.
Users could then continue to install their apps the way they are used to (using apt-get), since most of them do not care about the language their apps are written in or about other ways this application/library is made available.