Gambit Scheme especially has a great interface to C/C++/Objective-C. I've been happily using Gambit quite a bit for 20+ years, when it originated as gambit-68k for the Motorola 68000.
Gambit-C's been ported to iOS, Nintendo DS, etc.
In addition to the great C interface, it also has a great Unix/Posix interface, a great threads and message passing library (in the neighborhood of Erlang's performance for numbers of threads and messages per second), etc. It comes with Termite which is an Erlang-like programming model with mobile continuations.
So porting to Gambit provides some good avenues to explore.
-Patrick