Horizon is a parallel simulation extension of OMNeT++ that focuses on multicore and/or multiprocessor machines. Horizon employs a centralized (master-worker) parallel event execution scheme which uses a conservative synchronization algorithm. This synchronization scheme is based on a new modeling paradigm that annotates discrete events with durations in order to create an opportunity for parallel processing. Horizon was originally written for OMNeT++ 3.3, and has been ported to 4.x recently.
Horizon home page: http://www.comsys.rwth-aachen.de/research/projects/horizon/