I work in IT ... but I focus on Windows, Unix, Linux, FreeBSD, or Solaris on PC architecture. Supporting that, I know a lot of sites that feature open source software.
For anyone not familiar with "open source", this is community developed and supported software. It is made available free of charge to users, though applications based on open source code (example: a home inventory program that is built on MySQL database) may ask for or require a fee. I know many people using OpenOffice, a MS Office alternative, and many other applications very effectively. Well developed applications from this community can save computer users a lot of money and provide serious computing power.
Less familiar with Macs, I was happy to find this site containing open source software for Mac systems.
I'm posting the link in case it helps someone else.