{pico, tiny, nano}BSD, FreesBIE

Some people have asked me about why we have so many different
ways to make images..


I had a quick look for a page on the site that holds this
  sort of thing but didn't spot it..

Here's  quick comparison from my perspective.

In order of increasing size:

PicoBSD compiles from the given sources and can thus build cross
revision, or with a lot more tailored stuff.
Using the crunch gives TRULY tiny images.. (a 4MB image is
possible I think) A bit fiddly but the only way to go on a
machine with a really small image requirement.
I like it for [34]86 class machines with 8MB ram.
(If you can get a boot media)
it used to be possible to get it all on a floppy but I don;t think
that is now possible due to kernel growth.

NanoBSD compiles, and is capable of being set to build a cross image of
a different architecture.
Different compile options can be used from the build system,
e.g. you could leave out support for kerberos or similar and get a
different version of telnet.

TinyBSD uses the precompiled binaries on the building system. Thus it
can not make a crossbuilt image, or one based on a different
revision. (It does however make a custom kernel) It is however
REALLY fast.. It is interactive to some extent and can make an image 
which will run off the boot media or create a memory filesystem
image. (select at build time). In size it is similar to
NanoBSD but 'simpler', though less flexible. Still needs a little
work for running off a USB stick but works fine in mfs mode.

FreeSBIE is another option. it is designed to make not only a
basic image but to include all sorts of packages and possibly
configure them. Targetted at media the size of a CD.
it builds everything from scratch and can this be very tailored.
more flexible than tinyBSD, but more work too.

In addition there is Monowall and pfsense (monowall.org, pfsense.com)
though I haven't played with them.