Symmetric LISP
A parallel Lisp in which environments are first-class objects. It is implemented in Common LISP.
["Parallelism, Persistence and Meta-Cleanliness in the Symmetric Lisp Processor", D. Gelernter et al, SIGPLAN Notices 22(7):274-282 (July 1987)].
["A Programming Language Supporting First-Class Parallel Environments", S. Jagannathan, MIT-LCS/TR 434, 1989].