[mark_l_watson]

Although I don't use Java much anymore (favoring Ruby, Typescript, Haskell, Clojure, etc.) Java used to be my world, including enterprise Java.

Honest question: aren't there open source solutions for the best parts of Java Enterprise specs?

[SSLy]

GlassFish as mentioned is open source. Other commenter also brought WildFly, but it does not implement everything. I think you'd need jboss EAP. And there's TomEE++.

[Roboprog]

JBoss seems to work well enough. Er, Wildfly???

[punctilio]

WildFly is the project formerly known as JBoss Application Server.