You’d probably need to use a 3rd party service like LootLocker or roll your own in the cloud. If you’re not an experienced cloud programmer, look for a good 3rd party that you can use without having to rely on Steam or Facebook authentication. I used GameSparks in the past when I was shipping on iOS, Android and Windows Store, but they’re part of AWS now.
I’m currently doing all of my online stuff in Steam, including Achievements, Stats and Leaderboards, but if I decide to ship on other platforms, I’ll likely have to redo all that and migrate my data…