As Windows 10 development continues, Microsoft formally announced that the browser being developed under “Project Spartan”, will be called “Edge”.  It will be the default browser and will contain all the innovations.  IE11 will also ship as a secondary browser so that Windows 10 can still interact with legacy websites as needed

http://www.pcmag.com/article2/0,2817,2483459,00.asp

Among the many fascinating reveals in the opening keynote of the Microsoft Build 2015 developer conference—Android and iOS code running on Windows phones, holograms that can attach themselves to physical robots, and Visual Studio for Mac and Linux—was the Microsoft Edge browser.

Internet Explorer’s more modern and fast successor, previously code-named Project Spartan, is now Edge, and one of its most notable new features is extensions. Edge also maintains Spartan innovations like page markup, reading view, and Cortana integration. It’s also a Universal Windows app, meaning one application runs on PCs, phones, tablets, and whatever other Windows-running devices emerge.

Perhaps Edge’s greatest asset is that it’s not Internet Explorer, which, even after lots of improvements in speed and tightened design, was one of the most reviled pieces of software in history. Though Edge’s icon still sports an “E,” it really isn’t IE. Even underneath, it runs a new page-rendering engine called…wait for it—Edge. Yes, that was the name of Project Spartan’s engine, and it has now been elevated to the full product name. It tops IE’s longtime Trident engine in speed and compatibility with new Web standards such as HTML5.

Windows 10 will still ship with IE11 for legacy compatibility, especially for corporate intranets and other entreprise Web apps, but it won’t get new features and Edge will be the default browser.