This talk describes three Ruby usages: * Implementing high-level interface by Ruby. * Using Ruby as a glue language. * Embedding Ruby into a C program for flexibility. All of them have pros and cons. They are trade-off. If a case can ignore cons, we will have pros for the case. Most of Rubyists implement their Ruby applications only by Ruby. This talk shows another options to use Ruby as your convenient tool. If you know another options and trade-offs of them, you will implement your Ruby applications more effectively. This talk uses Droonga, a distributed full-text search engine, as a sample application to describe these Ruby usages. Droonga uses these three Ruby usages.