I'm have the Onyx Boox M92.

It is a 9.7" 16 levels of grayscale, 1200x825 E-Ink screen device running Linux & using Qt for the GUI (it even has DBUS inside! ).

It is totally independent on any bookstore and reads basically everything you can throw on it (ePUB, PDB, TXt, doc, PDB, CBR/CBZ, image files, ...) and even has several reader programs you can switch between, including the well known FBReader and Coolreader. On top of that it has a Wacom style pen tablet built-in so you can scrible & highlight your books/documents.

Regarding open source, I think basically all the source code is on Github and there is also SDK that can be used for writing applications.

Regarding interesting project with the Boox, someone ported Python on it and others are dual-booting Ubuntu and the original firmware on it.



For more info, see the M92 page on Mobileread wiki:
http://wiki.mobileread.com/wiki/Boox_M92