According to The Open Source Initiative, "Open source is a development method for software that harnesses the power of distributed peer review and transparency of process. The promise of open source is better quality, higher reliability, more flexibility, lower cost, and an end to predatory vendor lock-in." In lay terms, open source software is community-collaborative, which makes the code stronger and safer. Because of this, it's usually either free to individual users or much lower in cost than closed source products like Microsoft Windows, Office or FrontPage.
I wholeheartedly support open source software and the philosophy of community-collaborative development, software or otherwise, which is why my writing and my web site are open source driven. I recommend the following products:
Kubuntu development has progressed so far that the operating system is as fully-featured as any closed source rival like Microsoft Windows. It's easy to install and comes bundled with almost every kind of software you'd ever need for productivity. Your only associated cost would be that of commercial support and training, should you need it. However, the Ubuntu/Kubuntu forums are a rich repository of information, and if your answers aren't in the forums, you can create an account and post your questions. Someone will surely come along and help you out; open source folk are like that.
OpenOffice.org completely replaces the Microsoft Office suite of tools free of charge. Again, your only associated cost would be that of commercial support and training, should you need it. However, if you can install and use Microsoft Office, you won't need training for OpenOffice.org.
Even the Elder Gods need web sites, and when they do, they build those web sites with Cthrupal...er...Drupal. Drupal is an open source, database-driven CMS (Content Management System) that uses the PHP language and CSS to create dynamic, easily-updated web sites like mine. Yeah, you need to be a little tech-savvy to use it, but if you can set up a MySql database (or have your web host do it for you) and are willing to tinker with PHP and CSS, Drupal is a great web site option.
(Kudos to DrupalUK and Mr. Peter Brownell of Code Positive for this awesome graphic!)
FreeMind is the mind-mapping software I use to go from world-building to novel and short story outlines. It's java-based and available for both Windows and Linux. Honestly, I think it cuts my organizational time in half, which leaves me more time to write!
MediaWiki is the server-side software used to run Wikipedia. However, I have installed and used it on my PC in Linux. Again, you need to know how to set up a MySQL database to use this software (or have a good tech support team at your web host company), but the MediaWiki installation itself is straightforward. I have to say that my world-building was completely out of control until I started using a wiki to organize it. I wouldn't be without MediaWiki or FreeMind now.