Downloads are available from circuitpython.org. The site makes it easy to select the correct file and language for your board. The downloads page is here. Downloads are no longer available from the GitHub release pages because of the large number of files for each release. (If you see the unstable release 6.0.0-rc.2 when you browse circuitpython.org, that release is older. Use this one.)
To install follow the instructions in our new Welcome to CircuitPython! guide. To install the latest libraries, see this page in that guide.
Try the latest version of the Mu editor for creating and editing your CircuitPython programs and for easy access to the CircuitPython serial connection (the REPL).
CircuitPython has a number of “ports” that are the core implementation for a variety of microcontroller families. Stability varies on a per-port basis. As of this release, atmel-samd, nrf, and stm for the F4 family are stable. cxd56, esp32s2, and stm for other chip families are being actively improved but may be missing functionality and have bugs. litex and mimxrt10xx are in an alpha state and will have bugs and missing functionality.
Thank you to all who used, tested, and contributed since 5.3.1. See the 5.4.0 and 6.0.0 alpha, beta and RC releases for all who contributed. Join us on the Discord chat to collaborate.