Have you tried JRuby? It might be a bit too large for your droplet, but it has the java versions of most gems and you can produce cross-platform jars using warbler.
And yet operating distributed systems built on it is a world of pain. Elasticsearch, I am looking at you. Modern hardware resources leave the limitations of running/scaling on top JVM to be an expensive, frustrating endeavor.
In addition to elasticsearch's metrics, there's like 4 JVM metrics I have to watch constantly on all my clusters to make sure the JVM and its GC is happy.
In-house app that uses jdbc, is easy to develop and needs to be cross-platform (windows, linux, aix, as400). The speed picks up as it runs, usually handling 3000-5000 eps over UDP on decade old hardware.
