AmForth-Shadow is a Forth system that is optimized for Atmel AVR microcontrollers. AmForth-Shadow is an independent fork of AmForth ever since the latter changed its license from GPLv2 to GPLv3. See:
10/30/2014 message - The Shadow May Have To Disengage From Its Body
AmForth-Shadow changes to AmForth trunk@1687, the forking point, are summarized in amforth-shadow.org.