Argus
A successor to CLU, from LCS at MIT. Argus supports distributed programming through guardians (like monitors, but can be created dynamically) and atomic actions (indivisible activity). It also has cobegin and coend.
["Argus Reference Manual", B. Liskov et al., TR-400, MIT/LCS, 1987].
["Guardians and Actions: Linguistic Support for Robust, Distributed Programs", B. Liskov <liskov@lcs.mit.edu> et al, TOPLAS 5(3):381-404 (1983)].