Ruby/GP is a genetic programming library in Ruby language. It's features are still limited, such as no multiple populations nor selection methods other than truncation provided. But it has its own advantage. Being totally written in Ruby, it is easy to modify or extend the library by your own hand.
Even if you are not familiar with the domain, you can enjoy sample programs. Several famous problems of genetic programming are ready to be solved,such as "symbolic regression" or "artificial ant" and so on. And you can watch the codes to evolve as the generation proceeds.
Requirements: Ruby (1.6 or later)