[sehugg]

You don't need to necessarily have non-blocking libraries to take advantage of the async I/O. Netty uses worker threads to prevent blocking the server event loop and I assume Vert.X does as well. You can do blocking JDBC queries, Redis, etc.

As far as concurrency, most libraries state in the docs what is threadsafe and what is not, so this is more or less "caveat emptor" and RTFM.

Vert.x has its own module subsystem which appears to package up .jar files and some glue code for the Vert.x-specific interface, but I assume you can call any included Java classes directly: http://vertx.io/mods_manual.html

(Interestingly enough, Vert.x uses Gradle for its build/dependency manager, but I guess wanted something more Node-like for its module system)