These downloads are for outdated versions, which are no longer maintained.
For current and newer versions, please go to the web site for Racket.
Package:   DrScheme
Version:   4.2.1
Platform:   Macintosh OS X (Intel)
Type:   Disk Image
File:   plt-4.2.1-bin-i386-osx-mac.dmg
Size:   40Mb

Download links:     (Choose the nearest site)

Installation instructions
Once you finish downloading the disk image file, some browsers will automatically mount it and copy the PLT Scheme folder to your desktop. Simply drag this folder to a convenient place in your system. If your browser doesn’t mount and copy it automatically, you will need to do so yourself.
(Software License)