Radio licenses, live plane and ship tracking, and a few tools.

• Ships & aircraftPlanes and ships, from ADS-B and AIS.
• License mapFCC-licensed transmitters. About 3.9 million.
• Callsign lookupWho holds a callsign. About 659,000 US hams.
• ActivityWho's making contacts, from the spotting networks.
• Grey lineWhen and where the bands open up.
• PropagationCurrent solar numbers and band conditions.
• HarmonicsAn online harmonics calculator.
• Grid squareMaidenhead grid, distance, and bearing.
• ReferencePlain explainers for the stuff these tools touch.