Instant Rails just add water!.
Curt Hibbs (he of the excellent one-click Ruby installer for windows) has issued a preview release of his new package Instant Rails:
Instant
Rails is a one-stop Rails runtime solution containing Ruby, Rails,
Apache, and MySQL, all preconfigured and ready to run. No installer,
you simply drop it into the directory of your choice and run it. It
does not modify your system environment. See the Release Notes for a
complete list of what is included.
The preview is Windows only but releases for other operating systems will follow. [Curiouser and curiouser!]