Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
Cell Signal Monitor - Cell Signal Monitor is an advanced network monitor that helps you to watch the state of cellular network by gathering data about cell towers. The app supports GSM, UMTS and LTE networks. There is a Free edition with adds.
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
OpenSignal - Mobile analytics and insights on wireless connectivity from Opensignal, the independent global standard for understanding the true state of the world's mobile network.
Ettercap - Ettercap is a suite for man in the middle attacks on LAN.
NetMonster - NetMonster is a networking app by Michal Mrocek that comes up with features to enable you to get detailed information about your current network right on your mobile phone screen.