Robin is a language drawing from Pixley, Erlang, and PicoLisp. One distinctive feature of it is that it has an extremely small core semantics, to the point where even closures are defined in terms of macros. Another distinctive feature is that it is heavily resource-oriented; almost everything, including concurrent processes, is (or should be) a virtual device which must be acquired from a central resource arbiter. This arbiter may satisfy the constraints you specify when requesting a device any way it sees fit; so the operating environment has potentially a lot of influence over exactly what your program does.
Robin.lhs in the Robin distribution