The Raspberry Pi Pico is the MCU development board that uses the chip RP2040, designed by Raspberry Pi in 2019.

It is intended as a low-cost, low-power device with big computational possibilities and connectivity features. This device is intended to work with constrained power sources, mainly battery-powered. The MCU integrates all features, including 6 banks of RAM, an interrupt controller, DMA, timers, oscillators, I/O, voltage regulator and ROM in a single enclosure.
A compact, 7x7mm chip exposes 26 GPIOs and is one of the most affordable MCUs, estimated at 4 USD/piece only.

Currently, there are 2 types of development boards available: Raspberry Pi Pico and Raspberry Pico W. The last one provides wireless connectivity. It is also possible to have just MCUs (RP2040) as chips to be soldered, and thus, there are third-party development boards available in the market.

As there is a built-in voltage regulator, the input voltage range is wide and starts from 1.8V up to 5.5V.

The CPU is an ARM Cortex-M0+ (double core) running up to 133 MHz (scalable). It supports DMA. There is no FPU, however.

RPI Picos have 264kB of internal RAM, and 2MB of built-in QSPI flash with the capability for an extension with external one up to 16MB. RAM uses DMA to perform CPU-less transfers.

Only the Pico W series includes a built-in radio that is 802.11n (2.4 GHz WiFi) and Bluetooth 5.2.
IoT-specific protocols are supported only with external modules.

The nRF SoCs are equipped with a rich set of peripherals, including:

  GPIO – General Purpose Input Output lines
  TWI – Two Wire interface that can work in both master or slave mode
  SPI – Serial Peripheral Interface working in master or slave mode
  UART – Universal asynchronous receiver/transmitter
  Timer – timer/counter unit
  RTC – Real-time counter
  WDT – Watchdog timer

In selected models, additional units are available:

  QSPI – Quad SPI and high-speed SPI in some versions
  I2S – Inter-IC sound interface
  USB – Universal serial bus device
  PDM – Pulse Density Modulation (PDM)
  PWM – Pulse Width Modulation
  COMP – Analog comparator with low power version LPCOMP
  SAADC – Successive approximation analog-to-digital converter

All peripherals are connected to the processor via PPI (Programmable Peripheral Interconnect), ensuring flexible use of units. Peripherals have input signals Task that trigger their operation and output signals Event, which inform of some situation. These signals can be connected, creating hardware dependencies between units, making it possible to synchronise the operation of peripherals without the need for processor use. Some units can be handled with an internal DMA mechanism (EasyDMA) that supports data transmission between peripherals and memory without code execution. To enable safe wireless transmission, some cryptographic hardware units are included:

  RNG – Random Number Generator
  ACL – Access contol list
  AAR – Accelerated address resolver
  CCM – Cipher block chaining - message authentication code
  ECB – AES electronic codebook
  Cryptocell

The Cryptocell is a particular security subsystem developed by ARM®, which provides a device's root of trust (RoT) and cryptographic services. Hardware summary

[pczekalski] RP2040 description