As we previously reported, Spartan is a Windows Store application, and we can confirm that it will be replacing the current Modern version of IE that is included in Windows 8.1. Spartan will support Flash as well; this was a common question we received and can confirm that some versions of the browser do support it. We say "some versions" as the platform you are on will determine which features are available to you.
Spartan will be the browser across all of your Microsoft devices, from Windows 10 Mobile (Windows Phone) to Windows 10, and eventually onto your Xbox; this is Microsoft's new Modern browser. And because Modern apps now work on the desktop in Windows 10, Spartan could very well be your choice of replacement for Internet Explorer.