APK's are Android Applications. Think of an .exe, but for Android. As for the speed of things, what browsers are you using? It should run really smoothly on any recent (3-4 years ago or newer) computer. Now for the mobile, it depends heavily on how you get it on there. Do you use Phonegap or CocoonJS? PhoneGap isn't really built for mobile gaming. But in time, hopefully HTML5 will grow on the mobile field. But for now, it's best used for browsers or Windows .exe binary.