Ruby-OpenCL is a ruby binding of OpenCL,
which is the open standard for parallel programing of heterogeneous system.
It provides classes for OpenCL programing on host, not that on device.
Note that the Ruby-OpenCL is still Beta version.
http://rubyforge.org/projects/ruby-opencl/
Download from here.
You can get the newest version from SVN repository.
svn checkout http://ruby-opencl.rubyforge.org/svn/
A simple sample is here.