There are many great way to use JRuby, but one of biggest some is for glue between Java world and Scripting (, Lightweight, user-friendly or...) World, I think.
We, Treasure Data: data processing service company, have some good example for this case, Norikra and Embulk. These two OSS product have completely different purpose and architecture, but both have very similar mind for using JRuby.
I'll talk about what these software are, why/how these software uses JRuby. and also about the community around these software (especially in Japan).