ESP32 is available in 2 versions 38 pin & 30 pin.
ESP32 has total 48 GPIO pins, only 25 of them are broken out to the pin headers on both sides of the development board. These pins can be assigned to all sorts of peripheral duties, including:
 
15 ADC channels
15 channels of 12-bit SAR ADC’s. The ADC range can be set, in firmware, to either 0-1V, 0-1.4V, 0-2V, or 0-4V
2 UART interfaces
2 UART interfaces. One is used to load code serially. They feature flow control, and support IrDA too!
25 PWM outputs
25 channels of PWM pins for dimming LEDs or controlling motors.
2 DAC channels
8-bit DACs to produce true analog voltages.
3 SPI & 1 I2C interfaces
There are 3 SPI and 1 I2C interfaces to hook up all sorts of sensors and peripherals.
9 Touch Pads
9 GPIOs feature capacitive touch sensing.
 
ESP32’s pin multiplexing feature (Multiple peripherals multiplexed on a single GPIO pin). Meaning a single GPIO pin can act as an ADC input/DAC output/Touch pad.