GemPlugin is a system that lets your users install gems and lets you
load them as additional features to use in your software.  It
originated from the Mongrel (mongrel.rubyforge.org) project but proved
useful enough to break out into a separate project.

GemPlugin works by listing the gems installed, and doing a require_gem
on any that have the right dependencies.  For example, if a gem
depends on "gem_plugin" and "mongrel" then it will load as a Mongrel
plugin.  This makes it so that users of the plugins only need to gem
install (and maybe config a bit), and plugin authors only need to make
gems.