Basically a command-line mesh-debugging tool :-) Recommended by Freifunk wiki.
"horst" is a small, lightweight IEEE802.11 wireless LAN analyzer with a text interface. Its basic function is similar to tcpdump, Wireshark or Kismet, but itâ€™s much smaller and shows different, aggregated information which is not easily available from other tools. It is mainly targeted at debugging wireless LANs with a focus on ad-hoc (IBSS) mode in larger mesh networks.
AirView Spectrum Analyzer
This is a non-libre tool that comes with Ubiquiti's AirOS (that all of their routers run).
It can show both real time and averaged views of power levels (in dBm) plus a waterfall diagram view.
For the Ubiquiti Bullet M5, it operates at frequencies from 4.9 to 6.4 ghz.
It is a Java Web Start tool. Runs fine on Linux.
Console-based signal strength indicator.
aptitude install wavemon