Well, it's not the software side that's difficult. Generally, it's the user interaction story that's troublesome. In terms of games, it generally a question of

Well, it's not the software side that's difficult. Generally, it's the user interaction story that's troublesome. In terms of games, it generally a question of console, mobile, and PC/Mac. In that sense, the size of screen, the controller and/or gamepad versus keyboard/mouse versus touch input. Each will give players different advantages than players on other platforms. It's a bit more difficult to do cross-platform game and keep it consistent, fun and fair - even more so for multi-player online games. If only it were simply a question of just porting the software, then we'd see a lot more of it, IMO. Also, in regards to cross-platform frameworks and games: it's the additional latency, as well as the overhead (but almost certainly the latency) of any cross-platform compiler/library/framework that kills things. Games are right on the edge of a 12 millisecond per frame boundary (or less!) and every cycle usually counts for games these days (especially on limited mobile processors).