This is a user-space C implementation of Simplemux, a multiplexing protocol designed to improve efficiency and reliability in packet-switched networks. It provides two main functionalities: (i) traffic saving, by aggregating small packets into larger ones to reduce bandwidth consumption and packets per second; and (ii) fast delivery grant, by redundantly sending critical packets to minimize latency over unreliable links. The implementation includes three flavors (compressed, fast, blast), multiple transport modes, Robust Header Compression, and configurable multiplexing policies. Simplemux has been applied in research on online gaming, VoIP optimization, and smart grid communications. Simplemux is a protocol able to encapsulate a number of packets belonging to different protocols into a single packet. It includes the "Protocol" field on each multiplexing header, thus allowing the inclusion of a number of packets belonging to different protocols on a packet of another protocol.