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.