RawThumbnailer is a thumbnailer for RAW files that works with the Gnome Nautilus file manager. It is released under the GPL.
Known limitations
Not enough format are supported.
Download
0.99.1: .tar.gz - GPG signature
0.99: .tar.gz - GPG signature
Source code
Because this program is really for Gnome the source code is hosted in GNOME git repository:
git clone git://git.gnome.org/gnome-raw-thumbnailer