Downloading and installing the massive Xcode installer is a huge hassle if you just want GCC and related tools.
The osx-gcc-installer allows you to install the essential compilers from either pre-built binary packages or helps you create your own installer.
For Lion and Mountain Lion users, Apple now provides an official Command Line Tools for Xcode package that you can install without needing to install Xcode itself! You can download it from Apple's developer site (free registration required) and search for "Command Line Tools".
If you still need gcc-4.2, and you use Homebrew, you can install it using the apple-gcc42 package from homebrew/dupes.
You can download the installers on the Downloads page or use the links below:
To create your own package, place the Xcode Installer for your OS version (Install Xcode.app) in the root directory of the repository, then open the matching .pmdoc to build!
The source code from Apple for these packages is available here:
Do not install this if you already have Xcode installed! Mixing Xcode and osx-gcc-installer is known to cause various difficult-to-diagnose problems and is not recommended.
If you intend to only use command line tools you should first uninstall Xcode entirely before installing osx-gcc-installer, or see below for other options.