Freeware... because the software police will eventually carry mace.

Monitor your OS X (or OS X Server) hard drive/s. SMARTReporter runs in the background and periodically checks the SMART status of your hard drives.  SMART is a technology installed in the firmware of hard drives which detects hardware failures, or impending failures.  SMARTReporter can be set to popup alerts or send an email if there is a problem.

Mac OSX, Windows, Linux
The GNU Image Manipulation Program. Or as I like to think of it as the open source equivalent of Photoshop. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages.

Angry IP Scanner
Mac OSX, Windows, Linux
Angry IP scanner is a very fast IP address and port scanner. It can scan IP addresses in any range as well as any their ports. Useful in analyzing firewall rules and security concerns. It is cross-platform and lightweight.

Mac OSX, Windows, Linux
The open source alternative to Microsoft's Office suite of programs.  I have been using the software for a couple years, and have been amazed how quickly it has matured. Open Office can read/write the common Microsoft formats (.doc, .ppt, .xls), and has the useful ability to save slide shows as flash movies.  Unfortunately it is not an OSX native program and must be run inside the the X11 window system.  I recommend NeoOffice for the OSX folks.

Mac OSX, Windows, Linux
Njam is a full-featured cross-platform pac-man-like game

A program which helps in the creation of OSX installer packages (.pkg files). Combined with Apple Remote Desktop, package files can be a powerful tool in the management of large scale Mac deployments.

 Img2icns is a converter tool for your images. Enjoy creating thousand of icons from your pictures.

Makes time-lapse photography/movie making extremely easy using the built-in iSight on the new macs, or any attached camera. Just input the interval between frames, and what movie output you would like. Interesting also is it's ability to attach to remote cameras attached to other macs through bonjour.

Mac OSX, Windows, Linux

This open source email client is maintained by the same community that develops Firefox (Mozzilla).  It is a very clean and easy to use email program.  Basically all the best parts of Outlook, without the clutter.

Bonjour Browser
The application will scan the LAN for any nodes which are Bonjour enabled, and present them in a single window.

The ultimate web programming and design test tube.  Both WAMP and MAMP are self-contained environments running Apache, MySql, and PHP.  Meaning you can develop "traditional" websites and/or complex CMS web portals from the comfort of your personal computer. No knowledge of setting up web servers is required. WAMP is for Windows, and MAMP for Mac folk.

Mac OSX, Windows
A helpful program for people in charge of maintaining or repairing Apple products.  It is basically a database of all the specifications for every Apple product ever made. Constantly updated with new products by the developer.

There are many system utilities people have written to access the hidden command-line options in OSX.  Onyx is my favorite of the bunch.  It allows you to do such things as show hidden files/folders, deactivate dashboard, alter the login window, increase the speed of Safari, clean every cache, run maintenance scripts, etc.

JumpCut and Clipboard Buddy

Mac OSX, Windows
Both programs are what is commonly called clipboard-buffers. This means they will quietly sit in the background on your computer and store things that you cut or copy to the clipboard. After using one for a bit you will find yourself wondering how you ever got by with only copy/pasting one bit of text at a time. JumpCut is for OSX and Clipboard Buddy is for Windows.

Windows, Linux
One piece of freeware I really wish they made for Mac. Wink is a Tutorial and Presentation creation software, primarily aimed at creating tutorials on how to use software (like a tutor for MS-Word/Excel etc).  Since you can save in flash format Wink makes it extremely simple to publish your tutorials to the web.

Free Ruler
The name says it all. Measure things in pixels, inches, etc with this nice looking screen ruler. Found it helpful for object placement in web development. And in the creation of object reports for powerschool.

A simple yet powerful backup utility for Windows.  Can be used to backup or synchronize critical folders to backup drives, or network shares.  Contains many advanced options like email notifications, encryption, compression, filtering, and will even close active programs if you like.

A favorite of elementary teachers who take large amounts of pictures.  Galerie is an easy way to make great looking web pages to showcase pictures.  Just point the program to either a folder of pictures or iphoto album, specify a few settings, select a template, and the program will create a nice looking web site with click-able thumbnails of the photos.  All you have to do to publish is throw the entire folder created on the district web server.  There are a large number of user created templates you can download from the publisher's web site.

Help Quicktime be all that it can be with Perian. This utility will allow Quicktime to play a wide range of video formats it otherwise would not support, like the popular DivX.

Camino is an OSX only web browser which combines the look of OSX with the Gecko rendering engine (used by Firefox). Definitely worth a look.

An excellent addition to any elementary school who uses locally managed accounts in OSX and has students manually mount their home folders.  Just put MyHome in the dock, and no more "I forgot how to get to my server."

What could be better than the free feature-rich OpenOffice program suite?  How about an OSX native  version (no need for X11)!  In addition to word processing, spreadsheets, and presentations with NeoOffice you can create drawing documents, HTML pages, business cards, and master templates.