This is the SimGrid project.

There is at least 5 sub-projects in the tree:

 - XBT: eXtended Bundle of Tools (low-level toolbox: logging, datatypes).
 - SURF: a SimUlation aRtiFact. This is the simulation kernel.
 - MSG:  originally MetaSimGrid, MSG is a simple distributed application
         simulator.
 - GRAS: Grid Reality And Simulation (message passing API with two
         implementations allowing to compile programs on top of the
         simulator or for the real life without code modification)
 - AMOK: Advanced Metacomputing Overlay Kit (high level toolbox; Grid
         application elements such as distributed database, topology
         discovery service, and so on)

More informations are available in the doc/ directory.

In particular, don't forget to read the FAQ in there. It probably contains
the answer to your question ;)