Installing on OSX
There are three main approaches to installing Solfege on Mac OS X. None of them are easy, and they probably require some experience in compiling programs. All X11 and Xcode (aka Developer Tools).
Use MacPorts This is a program that makes it easy to install and update lots of open source software. Solfege on MacPorts uses version 3.19.2 as of January 2011 (thanks to David Baumgold!).
Use Fink Fink is similar to MacPorts. Solfege on Fink uses version 3.14.10 as of January 2010. To install solfege, users must enable the "Unstable" branch of fink, by adding the following line in /sw/etc/apt/sources.list:
deb file:/sw/fink unstable main crypto
Compile Solfege yourself. This way, you can always get the newest version of Solfege, and you have more control over the installation process. The big drawback is that you have to install all the dependencies yourself. Unless you've compiled a lot of open source software before, this will probably be difficult and take a long time.