To get Red on your machine, simply download and save the latest stable version that corresponds to your operating system (OS) from here: http://www.red-lang.org/p/download.html. The download is named red-num (on Windows, the file also has an .exe extension), where num is the version number, such as 063. This small file (around 1 MB) contains the full Red toolchain, runtime library, and console source code, truly batteries included! It is that small because no external dependencies other than the OS are included.
Red's runtime library is written as a mix of Red and Red/System. At this time, the Red toolchain (compilers, linkers, packagers) still depends heavily on REBOL 2. For example, the current compilers for Red and Red/System are written in REBOL 2. The goal for version 1.0 or beyond is to remove this REBOL dependency, so that Red is completely self-hosted.