Lunscape - 1 browser, 3 rendering engines
Upon setup, you can select your default rendering engine. Geck or WebKit are known for their blazing fast performance when loading many web pages and web apps,. Or you can choose Trident if you frequently visit web pages that only work with Internet Explorer.
The browser also supports bookmarklets, has a built in screen capture utility, skins, and has a full screen mode. Lunascape5 Alpha also supports add-ons, but right not there aren't a ton of plugins available. Unfortunately it will not work with plugins designed for Firefox, Safari, or Internet Explorer.