NetStylus, a Windows client for Networktablet, is now stable enough that I feel comfortable spruiking it here. I've been using it on my Surface Pro 3 with marvellous results (or at least they would be marvellous if I could actually draw), but it should work on any device. It lets you choose touch, pen, or mouse input, and excitingly, as it's built on the Universal Apps Platform, should also work on up-to-date Windows Phones (though I don't think there are any in existence with a stylus yet..). It's Windows 10 only, and available in the Windows Store.
It will be free for a while, but eventually I will be selling it for $USD 1. (Half of any revenue will be dontated to Bitfire). Source code is available at http://github.com/akdor1154/WinNetSty. (I don't expect to make much money, to tell the truth I'm interested in how a paid app with freely available source code performs).