For Leopard users who would rather get the source using git instead of downloading a tar-ball, this is what you would do.
1. Go to a Terminal window and change to the directory where you want the source to live.
2. Enter the command: git clone
https://github.com/omnigroup/OmniGroup.git
3. Change to the directory "OmniGroup".
4. Enter the command: git checkout "MacOSX-10.5"
Git should give you this message: "Branch MacOSX-10.5 set up to track remote branch MacOSX-10.5 from origin. Switched to a new branch 'MacOSX-10.5'"
5. If you are in a bash, sh, zsh, or ksh shell enter the command: "csh" or "tcsh" to switch to a C-shell so that xcodebuild's "setenv" commands will work properly.
6. Enter the command: "./Scripts/Build Frameworks" to build Debug versions of the frameworks, or "./Scripts/Build Frameworks install" to build release versions of the frameworks.
You may get messages at the start about some missing directories, but these can be safely ignored.
I used this method to build release versions of the 10.5 branch and the build ran flawlessly. I originally cloned the repository to my Desktop and the final products were left in /Users/Shared/me/InstalledProducts.
I hope this helps anybody wanting to build Leopard versions of the frameworks.