The latest version is available on Sourceforge. Sourceforge should automatically detect the best download for your platform.
These instructions are for the in-development 2.0 series. Info about installing R3R 1.2.x is on a separate page.
R3R comes as an ordinary setup program, made by Inno Setup. To install, simply download and run the r3r-version-setup.exe file. To run, just activate the item in the Start menu or through the desktop icon.
To uninstall, use the Add/Remove Programs applet.
There are packages for the three major package managers (RPM, Debian, and Slackware).
Note that there is no binary for Linux running on non-x86 architectures, such as Power PC.
If you run an operating system/CPU architecture not listed above, want to customise the software, want to help out or create a derivative, etc., you'll need to compile from source.
Read the included documentation for how to build it.
You can check out the latest version through the git repository on SourceForge or on github.