Clearsilver is a "language-neutral" templating package with bindings for C, Python and Perl.
I don't have a good sense yet of when language neutral libraries become more useful or worth the overhead compared to than language-specific ones. I have a hunch this is a question software architects will have to answer more and more frequently w/Parrot and Mono providing cross platform language-neutrality at the runtime level. When is it worth the overhead? Why won't template::toolkit sweep the scripting language world? etc.
I've been enjoying jython for the last couple months, and especially the ease of translating Java class documentation and examples to working Jython. This documentation thing is something that's been painful using COM or .NET components in languages much different from the ones MS documents. Even trying to map XML parser examples from VBScript to JScript is a pain sometimes.
Being on ActiveState's Perl.NET mailing list, you get some appreciation for what a challenge cross-language anything can be. And an appreciation for the elegance with which Jython pulls it off. I hope the same holds true for Parrot and Ironpython.