I loved the "lost war world" feel of Zayth in the core book and Lure of the Expanse. The landships and possibilities for trade and crazy adventures. The party in my campaign have ended up focusing on other worlds but I was wondering if any other GMs had brought Zayth into their campaigns.

In the core manual, within the example endeavours, Zayth is described as a world known for manufacturing macrobatteries (and presumably other weapons of war) of a pattern not seen in Calixis. The nature of this unrecognized pattern isn't detailed but as I understand it, it's not of xenos manufacture, just old and/or different somehow.

Lure of the Expanse goes into a bit more detail about the world. Autoloading macrocannons instead of the manually loaded ones the Imperium uses.

There's an idea about how they might work in game terms in this thread: http://www.fantasyflightgames.com/edge_foros_discusion.asp?efid=123&efcid=3&efidt=330925&efpag=0#331063