TL;DR
ESP-SDR firmware transforms the ESP32 microcontroller into a Software-Defined Radio (SDR) capable of receiving signals in the 2.4 GHz and 5 GHz frequency bands, all without needing extra hardware. This open-source firmware allows users to access the internal Analog-to-Digital Converter (ADC) of the ESP32 to capture raw In-phase and Quadrature (I/Q) samples, which can then be processed on a computer via USB or UART. It supports various ESP32 chips, including the ESP32-C3, ESP32-C5, and ESP32-S3, among others.