I mostly do so in Common Lisp, which gives me the performance of C with the productivity of Python, and the ability to extend the language with macros. But, having used it for nearly 20 years exclusively, I have recently started looking for other languages, primarily to learn all the different ideas there are out there.
Nothing complete enough, or interesting enough worth publishing yet :)
I'm a researcher mostly, so just like to implement cool graphics techniques in academic papers :)
Haven't made much of anything I would call an application, but I would like to one day.