YAML is a significant ruby library. It is used generally, like as RubyGems and RoR, etc.
To implement YAML processor by pure ruby, that means it can be used by most alternative ruby implementations directly.
Actually, RbYaml (http://rubyforge.org/projects/rbyaml) is a 100% ruby YAML processor already. But it was not widely used by most of the ruby implementations. I think it may caused by performance and comprehensive YAML 1.1 supporting. And there's no maintainer for RbYaml now.
So, base on RbYaml, I want to improve that, making a YAML parser and emitter that can satisfy present YAML standard more comprehensively. Then try to improve the performance.
After that, it will become a good choice for various ruby implementations, just like CRuby, rubinius, JRuby and XRuby.