If you're an OS X user who spends as much time on the command line as you do in the GUI, you're probably familiar with the MacPorts and Fink package management projects, making open source software easier to compile and run on Mac OS X. You may also be well-aware of the shortcomings of these projects when it comes to future-proof package management. A new, open source project called Homebrew may be exactly what you've been looking for. If you're not a lover of all things CLI, send a link to Homebrew as a great (free) last-minute gift for the Terminal-lover in your life.
My favorite thing about Homebrew is its ability to function perfectly well with /usr/local as its base directory, installing packages in their own folders but linking them to /usr/local/command. This makes them manageable with existing command line tools. Homebrew can work out of any directory you like, if /usr/local isn't your cup of tea. Installed packages are optimized and stripped based on your architecture, and makes great use of libraries you already have installed or that came with the system, reducing duplication and speeding up download, compile and install times significantly. Add in the zero-config installation, an already-extensive list of "formulas" (packages), a greatly-reduced need to
sudo anything, and a Ruby-based framework for creating your own formulae and you've got a killer package for extending your command line toolset.
Homebrew is available for free on GitHub, and the main page has complete instructions for various types of installation (and reasons why you'd pick each one). Check it out, and have a merry CLI-mas!