> The real-time collaboration seems kind of cool but also makes me wonder how you handle history, permissions, etc. If I'm editing code and you're editing code and I hit 'RUN' I don't want your half finished code that doesn't compile to prevent me from running the game.

Script changes are marked as drafted until you explicitely choose to apply them to the current build (Ctrl+S), so you won't break the build because you're in the middle of typing a line of code. There'll be a membership and rights system, right now there's only a server-wide password. Real-time script editing uses the same tech behind google docs and such (operational transform). There's no special history support right now, the server owner can version the projects in Mercurial / Git manually. Later on we'd like to have a project-wide revision system right in the UI.

> I'm curious why I'd choose this over say Unreal (free), Unity3D (free), Source 2 (free). ok, they aren't 100% free but they're effectively free until you make money.

Unity, UE4 (and probably Source 2) are multi-GB download and fairly heavyweight tools with sooo many options and drawers. Don't get me wrong, I love Unity (haven't spent much time with UE and Source 2 isn't out yet), but Superpowers is competing with Game Maker, Construct and the likes, not the big engines.