Lambda the Ultimate

Reform Prolog is a recursion-parallel implementation of Prolog. By executing all invocations of a recursive predicate in parallel, data-parallelism can be exploited. In contrast to most other parallel Prolog systems, Reform Prolog thus exploits structured parallelism; in contrast to present-day parallel Fortran systems, Reform Prolog can parallelize programs with procedure calls, pointer datastructures and arbitrary data dependences into doacross-style loops.

The Reform Prolog project ended in 1996 and somehow morphed into the High Performance Erlang project (which should be no surprise, as Erlang has clear roots in the Prolog world, though the concurrency model is different).