Veins - The open source vehicular network simulation framework.
Open-source implementation of the ETSI C-ITS protocol stack
ETSI ITS G5 GeoNetworking stack, in Java: CAM-DENM / ASN.1 PER / BTP / G...
A multi-stack, ETSI compliant, V2X framework for ns-3.
VEhicular NeTwork Open Simulator (VENTOS)