Deeplearning4j is the first commercial-grade, open-source, distributed deep-learning library written for Java and Scala. Integrated with Hadoop and Spark, DL4J is designed to be used in business environments on distributed GPUs and CPUs. Skymind is its commercial support arm.In essence, DL4J is a library for building "deep" neural networks, where "deep" apparently means more than one hidden layer. The software is open source (Apache 2.0 license). There is some free support available (from the user community, and possibly the developers). Commercial users needing serious support apparently can buy a support contract from Skymind.
Now, I don't know much about neural networks, although I do have some interest. Right now, I don't have time to put DL4J through its paces. Someday, if I find the time, I'll probably post some observations here. Meanwhile, I did download and install DL4J, along with the examples they provide, and I ran several of the examples successfully (and none unsuccessfully).
Their web site is very well done, with more links to general resources, documentation and tutorials than I think I've seen for any open source project before. So if the notion of coding serious (not just toy) neural nets in a JVM language appeals to you, I think you'd be well served to check them out.