"Release early, release often" they say, but at least release something that somehow works ;-)
When I started this, I had just squeezed raspbian down to 520MB (a 200MB .gz can be found there http://ygdes.com/Squeezed/ please be nice with my bandwidth and quota) but it was not automated and I had broken a few things. It's still usable over ssh or if you have a QWERTY keyboard but I'm not totally happy with it.
Now Jessie is out (of proportions) and I'm fighting with the dead weight. I learn to use resize2fs but the official image won't resize when the image in loop-mounted, for reasons that still escape me. I have conceded that a 8GB card is necessary during the image configuration, then resize2fs can be run on the skimmed card. So yes it can fit in 4GB.
This is not finished however but the beginning works so I put the scripts there http://ygdes.com/Squeezed/Squeezed.20151003.tgz
I know I have a weird coding style with bash and I hope you don't mind. It's just memories from an old Linux From Scratch-based project ;-)
The "hardening part" is not yet provided but it's a little procedure that is described in the previous log at the end of http://ygdes.com/Squeezed/install_20150926.txt