Gosh, the ms bashers are out in force.
Win 10 is aimed at everything. Windows 'proper' will work on everything down to 8". Yes, everything. Quite how it will work on Win7 devices I don't know, but at the moment it looks promising.
Below 8", contrary to opinions expressed earlier, is Windows 10 Phone. Which is, as near as possible to the full version. It is also to be launched this year.
From what I've heard from beta testers, it is truly impressive in the way that all Win devices talk to each other. You will be able to run full, proper Office on your 'phone.
MS have been left standing in that respect, but seem to have more than caught up.
It also fits loosely into the 'make one good one and then one terrible one' that MS seems to have as a proven track record.
Oh, and. It's free.