Raspberry Pi Pico is the new product announced today and it amounts to being a $4 micro-controller. The Pico is built around the RP2040, a microcontroller chip designed by the Raspberry Pi engineers. The RP2040 features a dual-core Arm Cortex M0+ processor with 264KB of internal RAM and support for up to 16MB of off-chip flash memory.
With this being all designed in-house, the Raspberry Pi Pico and RP2040 are extensively documented for the public so that this offering can appeal from hobbyists and tinkerers to other more formal micro-controller use-cases.
The Raspberry Pi Pico is available for $4 from Raspberry Pi partners. More details at RaspberryPi.org and the announcement that goes into great detail on the hardware's capabilities.