Pi calculus is an *(abstract VM) for parallel, mobile computations. Its basic version is very low-level, but already universal. _(Higher-order) versions encompass _(lambda calculus).

About Pi-calculus, I've found these pages:
<ul>
<li><a href="http://lamp.epfl.ch/mobility/">Calculi for Mobile Processes</a>.
<li><a href="http://www.cis.upenn.edu/~bcpierce/papers/#Pi-Calculus%20and%20Pict">Pi-Calculus and Pict</a>.
</ul>

There's at least one implemented language based on pi-calculus, <a href="http://www.cis.upenn.edu/~bcpierce/papers/pict/Html/Pict.html">PICT 4.1</a> (also <a href="http://www.cis.upenn.edu/~bcpierce/papers/pict/">here</a>).
