Jython 2.7 alpha1 released
fwierzbicki.blogspot.com
fwierzbicki.blogspot.com
What about Groovy?
(Corollary: what about .NET? Mostly I'm incredibly wary of recommending a language with only one "blessed" platform, and a proprietary one at that. My bosses are wary of this too: as a result of historical decisions we're currently locked into IBM hardware, writing million-line codebases in RPG-LE. If someone can allay my fears of vendor lock-in (at the hands of no less than Microsoft), perhaps I'll consider it.)
Also, for what it's worth, I was able to deploy full "Java" applications to the federal government that were completely Jython, and they've worked fairly well. The only concern I ever had was the one of how the customer might maintain such a codebase after our contract ended, but thankfully, that isn't a significant concern as a federal IT consultant, and super-tight deadlines often precluded Java as a viable language, only to see Java as a requirement later in the same RFP - This is where Jython (and its ilk) shine beautifully.
Edit: and just so it's said, I agree with your assessment on .Net. People are happy to pay for it, as well as the Microsoft tax, but I almost never saw it as the best option in a heterogeneous environment. It is also appreciably rare to run into an entirely Microsoft infrastructure.
I think one can make a case that Groovy comes pretty damn close, and at least as close as any other "scripting language on the JVM."
Platform: Well, it's the JVM.
Wide Adoption: Define "wide?" But from what I can see, Groovy is pretty popular, especially Grails. There are plenty of books on Groovy/Grails, Grails meetups / users groups in many cities, an active community of developers, etc. There are even consulting companies that focus on Groovy and Grails. SpanTree in Chicago, IL come to mind.
Familiar Syntax: Groovy is great in this regard, as almost any .java file can be renamed to .groovy and compiled with groovyc. Most of the syntax that's different between Java and Groovy is optional in Groovy, so you can start off writing Groovy that is very Java-like and slowly evolve to more idiomatic Groovy over time.
Maintainability: No better or worse than any other dynamic language, IMO. If you have access to metaprogramming and duck-typing and what-not, there opportunity for abuse is there. But Groovy's culture does not seem to be big on a lot of BFM.
hard to really fuck things up too badly - hmm... that's pretty subjective, but to that point, Groovy does have unit-testing tools, static analysis tools, etc. available. The ecosystem might not quite as rich as of that for pure Java, but I think you can find what you need to create a sane development environment.
You probably won't find many projects built "just" in Groovy - because of its JVM nature, you're more likely to find Java projects which are enhanced with Groovy (Groovy plugin for Hudson, for example, and the Play framework supporting Groovy in templates). Gradle as a build tool is starting to get some traction.
Groovy will probably be more behind the scenes than you'd like for a 'hey boss everyone is using this' sort of pitch, but it's not going away any time soon, and adoption is growing.
Biases on the table - I've done a number of mid-scale projects in Grails over the past several years, and I also run groovymag.com.
http://grails.org/Success+Stories
and note that Groovy is commercially supported by SpringSource, a division of VMWare. I'm guessing your boss has heard of VMWare.
As for wide adoption, Groovy's used in Grails but not many people seem interested in it as a standalone language. See O'Reilly's book sales for the year to March 2012 (http://radar.oreilly.com/upload/2012/03/Lang_QTR_Units_PrevY...).
I am optimistic you could pick .NET for Unix in a year or two
This really resonates with me. I feel like there's been a language boom in the past few years, but few implementations yet have the maturity and stability that I'd expect in a corporate environment. Given enough time and continued interest in alternative languages, I'd bet that Java's grip on this market will likely continue to erode (though an outright slide into obscurity seems highly unlikely). If it were ten years from now, perhaps I'd even be considering Go for this space.
source [1] http://en.wikipedia.org/wiki/Scala_%28programming_language%2...
You might have some luck with Groovy, but the performance hit might be an issue, depending on which types of applications.
On a former project I've found out it was easier to sell the Groovy than Python, due to the syntax being almost the same as in Java.
As for .NET I would only use it if you are only targeting Windows. Mono is not really an option for heterogeneous environments in the enterprise world, plus there are a lot of FUD discussions around it.
[edit] and many more: http://en.wikipedia.org/wiki/List_of_JVM_languages