So far, I've submitted only games as a Windows 8 developer, but I want to branch out to other services.
So, can I also submit games to Google Play, and the Apple App store?
absolutely you can submit to them all, but i not really sure if it can be submit to Apple App store.
Develop games in your browser. Powerful, performant & highly capable.
Check this tutorial for the apple:
https://www.scirra.com/tutorials/72/how ... -developer