Actually, you should qualify that a bit more. Ruby is rarely used outside of Ruby on Rails in North America. In Japan, it is widely used and Ruby on Rails is fair less common.

What were Ruby used for in japan?

Ruby is a very versatile language in its own right. While the other poster is correct that it is used for anything that perl and python are used for it's also taking a large chunk from the Java and C# crowd in Japan. Everything from server side applications to command line tools and even GUI based desktop applications can be written in Ruby. Using FFI I have made some quite amazing applications with Ruby.

Rails is amazing and I personally love it. But it's not the only thing Ruby is good for.

Probably anything that Perl and Python are used for.

Well, true, you have a point. Ruby is rarely used outside of Rails. Which is a shame, really.

Go to Japan.