Detailed instructions on getting rebol set up or installed.
The most mature and stable version of Rebol is the official Rebol2, available from the downloads page for multiple platforms. There are 2 flavors:
The version with gui (Rebol/View) is recommended for newcomers as it is also a super-set of Rebol/Core
As the download page states, Rebol requires no installation. Simply execute the binary you downloaded.