No matter how much the purveyors of shrink-wrapped software would have you believe it, there really is no reason to have to spend a small—or not so small—fortune on applications to run on your computer. That's not to say that the fine folks at Microsoft and all the other big name development shops don't put out some pretty cool tools, but an awful lot of what you want to do can be done with apps that don't cost you a dime.
Not so much an application, MacLibre is sort of a "greatest hits" collection of free software for your Macintosh. Now instead of running all over the place grabbing individual apps, you can download the whole pile all at once.
MacLibre includes productivity tools like NeoOffice (a Mac-ized version of OpenOffice), Internet tools and browsers, sound and graphics editors (Audacity and GIMP), and a bunch of utility apps as well. You could find yourself with a pretty well equipped system for the cost of only a few minutes worth of downloading.
MacLibre is distributed as a Universal Binary. That means that it'll run on both PowerPC and Intel Macs; you should be able to use it on systems that are running Panther (OS X 10.3) or later.