I get that open source means the underlying code is made freely available so any old geek can work with it, leading to improvements and add ons, but it's not as though I'm ever going to do that. To me, open source means free software that can compete with the big boys - and often blow them out of the water.
Mozilla's Firefox had tabbed browsing and the built-in ability to subscribe to website feeds long before the recent launch of Internet Explorer 7, as well as a huge variety of extensions and add-ons to give you more functions than you could possibly dream of. Adblock by itself cements the developers' place in computer geek heaven, since you never have to see popups or some other webpage ads. I also love Foxmarks, which synchronize Internet bookmarks between desktop and laptop.
The e-mail companion to the Firefox browser is Thunderbird, which made me forget Outlook as quickly as I'd forgotten Internet Explorer. You can use it for multiple accounts and it works as a great news reader too. This is where I subscribe to RSS feeds of my favourite sites and get new posts as if they were e-mails.
One thing it doesn't have is a built-in calendar to keep track of appointments and tasks, but there's a newish add-on called Lightning that fills that gap. Before that integrated option came along, there was Sunbird, Mozilla's stand-alone calendar. I preferred the paper calendar and chalk board above my desk to that more cumbersome choice, which offered far more function than my simple needs warranted. Plus, I guess I'm an old fashioned kind of computer near-geek.
When I got a new computer a couple of years ago, I decided to forgo Microsoft Office completely and give OpenOffice a try. It's the equivalent of Word, PowerPoint, Access, Excel, and Paint, with all the features I ever use, many I never use, and some bonus features like a built-in PDF converter. You can even save files as their Word, etc. equivalents - I set that as my default so compatibility with my Microsoft-bound office network is never something I have to think about.

The penguin definitely is cute, though. I just don't think that's quite enough to make me take the leap. Yet.