I've been fooling with implementing a runtime for a new language I call "Maverick".
It's an amusing testbed for techniques that will hopefully get me a few steps closer to the realization of a one-page implementation for a real, useful web application.
It uses a couple of interesting concepts. It attempts to enable gang-of-four style pattern-based programming. It incorporates AOP as a cornerstone and provides language-level support for nested transactions, persistence, role-based security and dynamic navigation. It also explores late-binding implementations reminiscent of Intentional Programming.
So far it's just a semantic runtime in search of a syntax and runs only on top of a JVM environment.