The title is incorrect: Azul are not open sourcing Zing JVM, they make it available for free to open source developers, but only for "development, qualification, and testing". Still nice though.
This is probably meaningless for most developers: it is only going to be made available "for use in development, qualification, and testing". Further, there's no information on what license this will be released under.
It's a shame, but given the amount that Azul has poured into research it is not surprising.
At least we can look forward to some interesting benchmarks and code analyses, perhaps?
As for the licensing, did Azul obtain a TCK from Oracle/Sun to say their JVM is for Java? If they did, it is unlikely they will open it up under a permissive license (e.g. MIT, BSD, Apache, etc).
One of Apache Harmony's big reasons for not obtaining and using the Java TCK is that it wouldn't allow them to release their JVM under the Apache license.
As at least some of you have figured out, the title is incorrect. Azul did not make Zing open source; we are just making free licenses available to developers working on open source projects.
Regarding performance, you can find some useful information on Azul's website. In a nutshell, Zing's strengths are its ability to GC while the application continues to run; and its ability to support very large memory heaps without a performance penalty. The two combine to permit a single JVM to do a lot more work and to avoid long application stalls when GC is triggered.
I believe we're somewhat constrained by our license with Oracle regarding what we can publish for benchmarks. But others are not, and this piece by Mike McCandless gives some good insight into what's possible with Zing:
