Microsoft has begun rolling out the second build (10051) of the Windows 10 Technical Preview for phones, which includes an early version of its Spartan browser for phones, along with a number of other features.

Microsoft's Windows 10 aims to resolve the present shortcomings in the user interface as well as unify the Windows, Windows Phone, and Windows Embedded product families around a common internal core. Microsoft has committed to launching the Windows 10 globally by this summer, but enthusiasts are more excited about its new default web browser, presently codenamed 'Spartan,' with a new rendering engine, dubbed 'Edge,' to replace the aging Trident-based Internet Explorer 11.

Last month, Microsoft had introduced the Spartan browser for Windows 10 being built in collaboration with several partners including Adobe, for desktops. Now almost two months after releasing its first technical preview of Windows 10 for phones, Microsoft has released the second build for testers, including the Project Spartan browser. Similar to the desktop version, Project Spartan uses Microsoft's new Edge rendering engine, but is not set as the default browser and exists side-by-side with Internet Explorer 11.

Microsoft has also introduced Universal app versions of Outlook Mail and Outlook Calendar, along with a new UI featuring a toggle that allows users to switch easily between the calendar and the email sections.

The release of the second build of Windows 10 for phones is significant, both in terms of features and the number of supported devices. The second build expands the list of devices compatible with Windows 10 Technical Preview for phones as the first preview (build 9941) worked on only six devices, while the latest build works on 35 devices.