Gimp is primarily used for editing photographs. It takes a little while to get used to where all of the tools are and how they work, but after that you are on your way.
Neo Office is primarily an office suite to help you from downloading anything made by Microsoft. It opens Word extensions and even includes a database program.
InkScape is a vector graphics drawing program. It does more than that, but it makes a lot of illustration work very easy. Be sure to go to youtube.com and search for tutorials.
Timeout is an alarm of sorts. When you turn it on it reminds you to 'time out' and take a break from looking at your computer screen. This is absolutely necessary for anyone spending any period of time on a computer.
If you want an absolutely wonderful, simple, time tracking system for anything Time Tracker is it. Designed with the Mac OS in mind with supreme simplicity and ease of use I highly recommend it. I use it because I work on so many different projects, but you could use it to track anything. You might like trying to track how much time it took you to work on a research paper to help forecast your next projects or you were curious how long you really spent on Facebook. Either way the price is right (free) and the software is amazing, so check it out!
I'm sure everyone has heard of FireFox by now, but if you have not download it on the link above. I love Safari, but I use FireFox when I am working on projects that require me to use two different browsers at the same time.
I still love Safari. Sometimes you get websites that just don't look right and it may just be your browser. Safari has the most premier viewing experience out of any browser in my opinion. The worst for security, clunkiness, and just plain bad is of course Internet Explorer. The FBI has been telling their employees not to use Internet Explorer for years.
I used to think that Gantt Project was the coolest thing ever for being free, but it is definitely superseded by Open Project. It has a format closer to Microsoft Project and is extremely user friendly. This is quoted from their website "OpenProj by Serena Software is a desktop replacement of Microsoft Project. OpenProj has equivalent functionality, a familiar user interface and even opens existing MSProject files. OpenProj is interoperable with Project, with a Gantt Chart and PERT chart"
I will keep updating this list as I continue to find cool business software that is free for the mac. For now check out another great list, much more comprehensive than mine so far: Chris Pirillo.