Most people use package managers for Mac OS X such as Homebrew or Fink to accomplish this. For older versions of Mac OS X you'll probably want to look at an archived version of Fink.
Macports works well for Leopard/ ppc. There are regular updates and many, many current versions of tools like git, python etc. are there. Having said that, there are also major gaps (e.g., the latest pandoc).
NetBSD's pkgsrc is actively updated and supports PowerPC. I use it on all my PowerPC Leopard systems. It works well, encapsulates everything cleanly and has its own system for starting and stopping daemons.