FlowTag is a GUI interface for exploring the TCP flows in a PCAP  
(network trace recorded by libpcap, tcpdump, ethereal, or wireshark)
file.  It's strengths lie in:

   * rapid reconstruction of flows (via indexing),
   * visual selection of source IP and destination TCP ports;
   * filtering by time, packet count, and/or byte count
   * tagging flows with keywords