Free antivirus for Windows & Linu personal users: AVG from GRISOFT

Free Windows spyware detection and removal program: Ad-Aware Personal from Lavasoft

Free online check to see if you are running old versions of programs that contain security vulnerabilities: Secunia.

Free firewall program for Windows (2000 & XP) personal users: Comodo Free Firewall Comodo also makes a a free antivirus program and a free backup program, which I have not yet tried. I also like the free ZoneAlarm.

Free graphics editor with most of the features of PhotoShop, for Windows and Linux and Mac: Gimp.

Free spam-filtering add-on for Microsoft Outlook: SpamBayes from Sourceforge.

Free Office Suite for Windows (2000, XP, NT), Linux, Mac OS X (under x11) Open Office from Sun. This suite includes Writer, Impress, Math, Draw, Calc, and Base.

Free Instant Messaging program that lets you talk to AIM, MSN, ICQ, and Yahoo Messenger friends from a single Windows program:  Trillian Basic from Cerulean Studios

Read PDF files for free: Acrobat Reader from Adobe

Create PDF files on Windows computers for free: PrimoPDF.

Use a faster, better Internet browser for Windows, Linux, and Mac: Firefox. Hundreds of free add-ons.

Free Email program from the makers of Firefox, for Windows, Linux, and Mac: Thunderbird.

Free Calendaring add-on for Thunderbird: Lightning. Thunderbird, with Lightning, provides much of the functionality of Microsoft Outlook, but for free.

Free control of your PC remotely:  Ultra VNC allows direct Windows-to-Windows use.  LogMeIn Free allows control of your Windows computer from any web browser. These compete with paid products such as Link2PC ($7/month), LogMeIn Pro ($13/month), and GoToMyPC ($20/month).

Handy free desktop sidebar software.

Receive faxes via your email program for free: eFax Messenger

Explore the earth for free: Google Earth

Find out where your wasted disk space on Windows systems is: SpaceMonger from Werkema

Free weather reports with no ads on your Windows desktop: Weather Pulse from Tropic Designs It uses weather data provided by the government. Some competitors trying to make bundles of money by selling advertising accompanying weather data are trying to pressure the government to stop providing weather data free to taxpayers.

Free sticky notes for your desktop: Stickies.

Free searching for your own computer files. Yahoo Desktop Search from Yahoo.

Free Media Players

Free MP3 player for Windows: Winamp Basic from Nullsoft

Free Divx Player for Windows: Divx.  (Divx is to video what MP3 is to audio--it compresses files to more manageable size.) An even better player is KM Player.

Good General Freeware Reference