Windows Insider Program

Windows Insider Program is a software testing program by Microsoft for Windows 10 and Windows Server. The user can opt in the program to test out new features and new versions of the operating system that were previously only accessible to developers. Three channels exist for the Windows Insider Program, these are Dev, Beta, and Release Preview (originally known as the Fast, Slow and Release Preview rings until June 2020). The first build that was released from the Insider Program was 9841. Microsoft also releases some builds in ISO format as well.

Channels
Dev Channel: This channel receives builds frequently, and are the earliest in a development cycle, and as such contain the latest code from the Microsoft developers. These builds are not recommended for daily use. They are not tied to any specific release.

Beta Channel: This channel receives builds less frequently, and are tied to a specific release of the operating system. Builds from this channel are more stable than the ones on the Dev Channel.

Release Preview Channel: This channel receives builds to Insiders prior to it being released officially.