Cyber-Physical Systems require the integration of various heterogeneous networks. To evaluate proposed algorithms in network research, real-world test beds are an indispensable complement to simulations. In this paper, we present a flexible heterogeneous mesh networking platform (FHMESH) which interconnects various heterogeneous networks, i.e. wireless sensor network, wireless mesh network, FM radio network and the Internet. FHMESH builds agile and universal gateways using software defined radio technology, and the gateways form mesh backbone to interconnect those heterogeneous networks. Then, we present the platform architecture and the specific implementation details for FHMESH, and carry out some preliminary experiments. Even though the testing results of our system are not so perfect, we believe that the integration of various heterogeneous networks makes FHMESH work as a prototype for heterogeneous network research, and the flexible and universal gateway can facilitate the cross-layer research.