Day-to-day I come into contact with a variety of operating systems, but my main desktop environment at the moment is Apple's OSX. I never thought of myself as one of those Mac zealots until I was forced to go back to Windows for a few days recently. Microsoft's aging operating system is really starting to look clunky and dated compared to the sleek design and usability of OSX and even some Linux distributions like Ubuntu.
While I've been using Apple's Tiger operating system for about a year now I thought it might be worth mentioning some of the more useful tools I use at work. Most of these applications below are freeware or open source.
Apple's Mail is pre-installed with OSX and is simply the easiest e-mail client to use in my opinion. Those who have a Microsoft Exchange server might want to try Entourage though.
While Safari is a very capable browser, Firefox is more widely supported by Web developers. The Firefox browser also has many handy browser plug-ins and toolbars which simply aren't available in Safari.
Microsoft Office for Mac
Okay, I know Open Office and Neo Office are both fine open source alternatives but it seems for true collaboration in an office environment which involves sharing excel and word documents then Microsoft's offering is just much cleaner and easier to use.
NVU is an open source visual text editor. It is probably comparable to Adobe's Dreamweaver tool, but more than does the job for what I use it for.
VLC(VideoLAN Client) is an open source media player that will play just about any format of video or audio you can throw at it. It's an easy way to get around unsupported formats that Apple seem not to support in their multimedia applications.
Adium is a free instant message application that will let you connect to multiple chat programs like Yahoo, MSN, and AIM messengers. It's arguably much easier to use than any of the native instant messenger environments written by Yahoo, Microsoft or AOL.
This isn't exactly work related but copying music to and from your iPOD should be as easy as dragging and dropping files. Unfortunately it's not that easy in iTunes which makes Senuti a handy tool for those who listen to music while working.
iTerm is a terminal program that runs natively on OSX. It's still in beta but a very handy tool for those who like to use the terminal.
If you are looking for more information about your wireless network or other people's wireless networks then KisMac is a useful tool indeed.
Transmission is a freeware torrent download client which is easy to use.