RMagick4J source is public domain, but it includes addition software. See LicenseInformation for more on the licenses.
You can install the gem at RubyForge? like so:
gem install rmagick4j
And then you can use it in your software like so:
require 'rubygems' gem PLATFORM == 'java' ? 'rmagick4j' : 'rmagick' require 'RMagick'
In a future version, the gem may be released simply as rmagick (well, rmagick-java), but for now the support is sufficiently limited that it has been deemed best to use a different name to make people aware of the difference.