Be careful with download.com as they have a lot of software that may be free but not all of it is open source.
A good reference list is Here.
The largest, moet well known projects are Openoffice and the Mozilla software such as firefox, Thunderbird, etc.
The reason I specify open source as opposed to just free software is the open source projects are more public. The source code is published in some sort of version control repository where not one single person owns. A lot of times freeware programs are someone thing one person has written in their spare time and the source is only held by them and a couple years later they get tired of doing it and quit and you then can't get any new versions of that software. Open source people may come and go all the time but the code is out there where someone else can pick it up and continue.
Since I rely on my computer a lot I've made some of my own standards to keep me prepared for anything, kind of how we never leave home without our PSK and talk about the x number of essentials for survival, I have some rules that are essential for my computing needs. Open Source and or Cross platform is one of the big essentials for any software I use now.
What has happened to me in the past is some software I've used, be it a free download or paid for package such as Microsoft Money, Visio, Office, Works, etc., is that sometimes the author of the free package will stop updating it or supporting it or with either the free or paid software I upgrade to a new version and the new version doesn't support the file format of the old so you have to keep running two versions of that package. Then you upgrade your (windows) OS and the old version won't work under the new OS so you have to run two computers, one with the new stuff and one with the old. Then you spend a weekend exporting all the data from the old version and importing into the new and cleaning up or filling in anything that got messed up or lost in the conversion process, then a couple years later realize you missed a file and go to your backups then have to find some way to get the old version of that software to read that one file, then find out that old version isn't available anywhere. So you start backing up the software with the data which takes more space and with old versions of paid for software your starting to breach the license agreements.
Much better to stick with the open source stuff. I have one CD with my standard software load, Firefox, Thunderbird, OpenOffice, Gimp, etc. That standard load goes on my laptop, my wife's laptop, my parents pc's, etc and gets burned and stored with my backups. Since its open source I'm free to make and install as many copies as I want with no legal issues. I'm also not limited to one OS version or even one OS. I can edit the same files on my wife's laptop running Windows XP or my pc running linux or some friends Mac or that old Solaris box I found in the trash. If I have to evacuate and loose all my computer equipment I can be back up and running on someone elses or a new one in a few minutes by either installing my software load from cd, downloading it from the internet, or running the portable version from a flash drive. Try and do that with Microsoft Office 97. You don't need to be very computer literate to do this, just be careful when choosing software and research it well, just like you would do for survival gear, be it a flashlight, knife, or PLB.