For anyone wondering, both clients work, as far as I can tell, without a hitch on Windows 10, including UO Assist and UO Cartographer. For anyone running Windows 7 and later, I would strongly suggest you set aside your copy of Windows 10 and take the free upgrade if it is offered to you. The upgrade process is fairly painless, and most things just work. For those used to either Windows 7 or 8/8.1, navigating around Windows 10 shouldn't be too difficult. I'm still on the preview (beta) version, and there is still a significant amount of polishing to be done, but I have noticed a slight improvement in performance over Windows 7 x64. For those on older hardware Windows 10 takes less space on your hard drive, once you clean up the update files, and has a smaller memory footprint. It should run better on older/slower hardware than either Windows 7 or 8/8.1 does. But the major reason to upgrade, in my opinion, is I expect support for both Windows 7 and 8/8.1 to end sooner rather than later. My feeling is that Microsoft is making a real push to get everyone on the same page in terms of operating system versions - hence the free upgrades, something unprecedented in Microsoft's history. And this is a full featured free upgrade that will upgrade you to the version of Windows 10 that is equivalent to your current version (Home, Professional, etc.).