Cam blogged IBM AlphaWork's Sash before I got a chance. I got a pretty extensive demo of Sash from one of its developers last week in Arizona when Tim O. brought me over to give him my opinion of it (flattering). From what I understand (and I understand neither that well), it's significantly different than Mozilla, in that it let's you do all kinds of funky things through the Windows API -- like creating dockbars, integrating with the file manager, etc. (all through JavaScript). Also, they just started with Windows ("because it was the hardest") but will also be porting Sash to a plethora of platforms. This isn't an endorsement, but I find it interesting and will be looking into it more.