[privacyfornow]

My recommendation is Vertx.io

It is a very lightweight framework with support for most of the plumbing a developer might want without imposing its will on anyone.

If you are not that worried about having a REST or HTTP or TCP front-end, LMAX disruptor is amazing as well.

[javajosh]

Have you ever made anything real with Vert.x? I found several aspects of developing for it problematic, such as it's rather odd module sysem.