Open-source software (OSS) is computer software with its source code made available and licensed with a license in which the copyright holder provides the rights to study, change and distribute the software at no cost to anyone and for any purpose. Open-source software is very often developed in a public, collaborative manner. Open-source software is the most prominent example of open-source development and often compared to (technically defined) user-generated content or (legally defined) open-content movements. Wikipedia
Not all the best things in life are free, but there are a lot of things which there doesn’t seem any point spending money on. Some software I use is proprietary (OSX, iOS, Pages, Blogsy etc) but I always believe in using the right tool for the job rather than using open source or a particular company just for the sake of it. My list of software is available here, and no doubt will be updated regularly.