Although all free software is, by definition, open source, not all open source software is free(speech). For example, PINE, POVray, ssh, and the like are all restricted, and the source code is basically how they make binaries available for all platforms; with those programs you cannot distribute modifications on your own, and in some cases (such as PINE) you can't even distribute your own binaries. This makes things funky for Debian, where it has its own way of keeping programs consistent in configuration; to get PINE on a Debian system, you have to download the unmodified source and then patch it with the Debian modifications to build your own binary. Very annoying.

POVray isn't quite so bad. Basically you can distribute patches and unofficial binaries but you can't fork or distribute modified source code, and the POV team also likes to sit on the latest-greatest modifications in the source distribution; lately they've only been releasing binary-only Windows releases. Yuck.