A *(Learning Lounge) course. 

The <a href="http://www.lfcs.informatics.ed.ac.uk/reports/91/ECS-LFCS-91-180/ECS-LFCS-91-180.ps">Polyadic pi-Calculus: A tutorial</a>: calculus of concurrent processes. The tutorial describes both monadic and polyadic variants.

The <a href="http://para.inria.fr/join/eng.htm">join-calculus</a>: yet another calculus of concurrent processes, along with a programming language. It's basically a declarative version of actor-oriented programming.
