TOP 5 FREE or OPEN SOURCE APPLICATIONS

1. UBUNTU (OS):  A Linux flavour that is easy to experiment with, includes a number of features right out of "the box" and makes it simple to locate additional applications to expand upon it.  It can also breathe life into an outdated PC or a inexpensive netbook.
2. DIGSBY/TRILLIAN or PIDGIN/ADIUM (IM):  All three clients (Adium is basically the same as Pidgin for Mac OS) are brilliant in some ways, but flawed in others.  Read my earlier post on comparing their features.  In a nutshell Pidgin/Adium is open source, cross-platform and is best for JUST IM - as it connects to virtually every conceivable protocol out there.  Digsby & Trillian are more limited to just the primary networks but also do email notifications, Facebook feeds, Twitter feeds (Digsby has a whole embedded client for Twitter), MySpace feeds (Digsby only) and LinkedIn notifications (again, Digsby only).  Digsby is still currently Windows only however, while Trillian is cross-platform a a bit prettier.  Both attempt to install junk-ware upon installation for funding, so check closely and untick any appropriate boxes.
3. VLC + DOUBLETWIST (media player): The lauded VLC Player can supposedly play ANY media file out there - audio or video, while doubleTwist serves as a brilliant alternative to Apple's iTunes and it's monopolistic grip.  doubleTwist includes such features as the Amazon MP3 store which is nearly as large as iTunes and usually with cheaper DRM-free pricing, a great Podcast search engine and touts itself as "iTunes for Android" - but it is also for nearly every other MP3 player and mobile phone, including iPods themselves!  There is also Songbird out there which was once a Mozilla project. This means it is of course open source and customizable with extensions as well, but it's features and gadget compatibilities are somewhat lacking behind doubleTwist.  I'm not so sure it is as well supported anymore as Firefox, Seamonkey, Camino and Thunderbird.
4. FIREFOX or GOOGLE CHROME (browsers): I have found my configuration of Firefox to be faster, sleeker and to take up less "screen real estate" than Google Chrome, but others swear by Chrome's speed and Firefox's bloated sluggishness or instability.  I believe that they comparing the clean version of Chrome to a Firefox that they have been using for years and jam packed with themes, add-ons and extensions to create an unfair assessment, but that's neither here nor there as both browsers are very well designed and brilliant.  I use them both interchangeably.  There are glitches and failings with Chrome that still annoy me (like certain pages don't render in it, Ad-Block doesn't really work with it as well as with Firefox, no native "Bookmarks" drop down menu button, no "Print" button?!?, no "Print Preview" at all?!? and you can't tile it in Windows) - but the sandboxing of tabs to prevent one page from crashing your entire browser and the amazing security of it's code are very impressive.
5. THUNDERBIRD + LIGHTNING  (PIM): If you don't have or use the FULL Microsoft Office version of Outlook and are stuck with the crappy "Outlook Express" or God help you "Entourage" then you'd be doing yourself a disservice by not using Mozilla's Thunderbird as your email client.  When you add in the Sunbird calendar extension called "Lightning" you will have a full featured PIM just like with Office Outlook!  Speaking of which, just like with Firefox, you can add extensions and themes to Thunderbird to expand and customize it's capabilities too!