Ruby C extensions will by default compile 2-way fat, for ppc and i386.
You can set the ARCHFLAGS environment variable to configure the build of an extension, if for example it links against a non-universal library (like the binaries which are delivered per processor architecture).
A: We updated 12 movies to reflect changes to Ruby on Rails, as of version 3.2, and to accommodate the release of version 4.0.
This includes updates to the Macintosh installation process, how you access a new project, loading stylesheets, and making model attributes accessible for mass assignment.
[..] The Ruby libruby.1.dylib library, which contains the core of the interpreter, is available as a 4-way fat universal binary, for the ppc, i386, ppc64 and x86_64 architectures.
You can therefore embed Ruby in a 64-bit application.
Some scripting elements are not yet accessible though, like enumerations, but most of the functionality should be available.