PLEXIL (Plan Execution Interchange Language) is a language for representing
plans for automation, as well a technology for executing these plans on real or
simulated systems. PLEXIL has been used in robotics, control of unmanned
vehicles, automation of operations in human habitats, and systems and
simulations involving intelligent software agents.

PLEXIL was designed initially to meet the requirements of flexible, efficient
and reliable plan execution in space mission operations. It is compact,
semantically clear, and deterministic given the same sequence of events from the
external world. At the same time, the language is quite expressive and can
represent branches, loops, time- and event- driven activities, concurrent
activities, sequences, and temporal constraints. The core syntax of the language
is simple and uniform, making plan interpretation simple and efficient, while
enabling the application of validation and testing techniques.

WWW: http://plexil.sourceforge.net/wiki/index.php/Main_Page