See also: article on extremely small interpreters for code density.

Hedgehog (http://hedgehog.oliotalo.fi/) is a variant of LISP for embedded chips released under a BSD (library) and LGPL (tools) license. It has some debugging tools and can run on x86 as well for development. The model is to compile bytecode on a development machine and execute it on the MCU; there is no REPL on the device itself. Developed and maintained by a Finish company (.fi TLD?) mostly for use distibuting new bytecode programs. Implementation is well documented.

PICBIT is one of a series (BIT and PICOBIT) of Scheme implementations for very small (few kb RAM) chips. Code is compiled to bytecode on a development machine and run/interpreted on the device. This is a mature academic project; there are a couple papers which summarize the approach and design decisions.

ARMPIT Scheme (http://armpit.sourceforge.net/) is a full embeded Scheme environment for ARM MCUs (including Cortex-M3s). It is an active project written in

ā€œLā€ is a Common LISP implementation for embedded MCUs with about a MB of RAM; it was an MIT AI Lab project. A real time operating system written in C (VENUS) runs on the metal and an L framework called MARS coordinates message/event handling between multiple agents. It was written for robotic research.