At face value, the open source software (OSS) proposition looks too good to be true. Free, or at least inexpensive, software applications that provide equivalent functionality to much more expensive proprietary products, backed up by thousands of software developers constantly working on upgrades and fixing bugs.
As ever, the reality is more complicated. OSS may usually be free and flexible, but it is still protected by copyright and licensed. To quote the Free Software Foundation (FSF): "Free software is a matter of liberty, not price. To understand the concept you should think of ‘free’ as in ‘free speech’, not as in ‘free beer’."