A new guide: CircuitPython on Raspberry Pi (Bare Metal / No OS) by Scott Shawcroft
The Raspberry Pi single board computers (SBCs for short) are normally used with the Raspberry Pi OS. This is great for gaming and web browsing, but isn’t designed for microcontroller-like tasks. Tasks like reading I2C sensors and SPI devices can be trickier. Furthermore, Linux system maintenance can be tricky for beginners.
Instead of Raspberry Pi OS, one can now use CircuitPython instead. CircuitPython running without another operating system (OS) is typically known as “bare metal”. This greatly simplifies system maintenance and makes it easier to treat the Raspberry Pi like a microcontroller. In addition, running CircuitPython on the Raspberry Pi increases the amount of flash and RAM available to CircuitPython programs. Finally, it also adds the ability to use displayio on HDMI displays.