Mole is a project mainly written in ..., it's free.
M0 Overlay LanguagE
This repo contains the beginnings of Mole, a new Parrot language which is being designed to generate the very low-level M0 langauge.
Mole is the future of Parrot. The point of Mole is to provide a medium-level language which will be comfortable for Parrot developers to code in. In the future, instead of writing Parrot internals in C, Mole will be used, which will be compiled down to M0 and then M0 bytecode. This will allow the amount of C that is in Parrot to greatly contract, which means crossing language barriers will be much less common and thus allow many optimization techniques to be applicable.
M0 is extremely low-level, and was never intended to be written by humans except during the bootstrapping phase. M0 was created because Parrot wants to implement an efficient JIT compiler, which is currently not possible do to the way Parrot internals (all the C code) are implemented.
M0 consists of roughtly 40 opcodes from which the rest of Parrot can be built from. Currently Parrot has over 1000 opcodes (due to supporting various combinations of argument types), which basically precludes the possiblity of implementing an efficient and maintainable JIT.
We don't yet know. It is currently in the design phase.