ALEF
A programming language from Bell Labs. ALEF boasts few new ideas but is instead a careful synthesis of ideas from other languages. The result is a practical general purpose programming language which was once displacing C as their main implementation language. Both shared variables and message passing are supported through language constructs.
A window system, user interface, operating system network code, news reader, mailer and variety of other tools in Plan 9 are now implemented using ALEF.