My favorite part of Maxthon was the rendering engine switching, where you got to change between Gecko and Trident, and it looks like even Webkit was supported at one point. This was back when you basically needed to use Netscape/Mozilla for modern standards and IE for sites that absolutely needed it. It seems like the only place in the years following you'd see this would be to get away from IE using forwards compatibility (Chrome Frame) or backwards compatibility (IE Tab in Edge).