QueSO
Remote O.S. detector. Sends obscure TCP pkts to determine remote OS. Fully configurable. Runs on Linux, Solaris and probably any OS with libpcap support.
C libpcap TCP/IP
[ ACCESS VIA BBS ] PROJECTZ
[ SOURCE CODE ARCHIVE ]
NePED
Network Promiscuous Ethernet Detector. Scans a subnet using hacked ARPs (non broadcast), only listened by promiscuous ethernets. The answer to hacked ARPs expose promiscuity (presume sniffer).
C ARP Raw Sockets
[ ACCESS VIA BBS ]