jNetStream is a sniffer and a protocolanalyzer. Includes applications and library. 100s of protocols are defined. Includes scripting. It is appropriate for custom protocol development, grad students, and network teachers/professors. Full SDK included.
NetworkTools has 2 components: A protocolanalyzer 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.