The Null-modem emulator (com0com) is a kernel-mode virtual serial port driver for Windows. You can create an unlimited number of virtual COM port pairs and use any pair to connect one COM port based application to another. The HUB for communications (hub4com) allows to receive data and signals from one COM or TCP port, modify and send it to a number of other COM or TCP ports and vice versa.
NetworkTools has 2 components: A protocol analyzer which plays a TCP client or server or pipeline, which sits between a client and server and shows how they communicate. A port scanner can scan a range of IP addresses and ports. See screenshots.