The document discusses various technologies for counting people in real-time, including vision analytics, 3D stereo video analytics, monocular video analytics, Raspberry Pi or Arduino, WiFi tracking, thermal imaging, infrared beams, structured light, time-of-flight sensors, ultra wide band radar imaging, Bluetooth beacons, GPS trackers, drone cameras, RFID tags, facial recognition, augmented reality, and using depth sensors to count people in cluttered scenes in real-time. The counting of people presents challenging tasks and benefits from multiple camera angles and cross-camera knowledge transfer.