Some of the Icons in Windows 10 are just fonts. Thanks to a great idea by Vadim Sterkin to replace the Windows 10 Font with that of the Preview Builds of Windows 10 we can no activate those new icons on all versions.
Microsoft teased some new windows icons a few months ago. This month they went into beta and now we see the first ones released to the public.
Recently Microsoft revealed the new icons for office 365. They look much better the the ones we have now. You can download some of them here!