HTML5 is cross-platform, but not natively.
Also, this may be just me, but I do not take too kindly to playing games in WebBrowsers.
OK, I actually anticipated this response. That's why I planned the HTML5 engine to be general purpose enough to use in multiple games, not just this one -- so that my time won't have been wasted if it doesn't get used by this project.
The thing is, I have other uses for a HTML5 2D Tile based engine, and was attempting to kill 2 birds with one stone by using this project as a flagship. So, I'm going to continue building the Mason Engine, for building collaborative 2D tile worlds. Whether folks choose to use it is up to them.
The protocols are being designed with client side abstraction in mind. That means you could build a radical new native client in any other language in the universe in addition to the HTML5
web engine, and have both native and web browser options.
I don't think a 2D Tile based roguelike-ish game requires the power to justify the risk of downloading unsigned binaries from strangers and running them on your PC natively... Going to a website and editing and playing the game is a far lower barrier to entry, IMO.
I already have my own 3D cross platform native projects in the works, so spending my time programming this in C/C++/Java, etc, just isn't appealing to me personally. Native 2D tile engines already exist (download Nethack and replace the game data, you're done). I'd rather put my effort into bringing new collaboration features to the community rather than using an existing engine like Unity3D which I have no source code for, and don't have the freedom to extend. If Unity goes out of business my time spent developing for their closed platform will have been wasted, so I personally would use SFML or SDL, it's not like you need Unity's features for a tile engine; I mean, unless we make the game a 3D adventure or something.
Don't get me wrong, It's fine with me if folks want to go the native route instead, and I'll still contribute in other ways, but I won't be able to contribute any time writing code for the project if it's a native only codebase.
Additionally, This forum serves as a public record and keeps things out in the open and recorded for all to see. I don't think Skype should be required for anyone to contribute. I don't run closed source software made by people I don't trust, so I won't be able to use Skype either -- IMO, that seems like an arbitrary requirement. What about an IRC chat room or an open source VOIP solution instead?
Note: I work and sleep weird hours because most of my business is with overseas clients. That's another reason a forum seems the best option to me -- Folks can collaborate without being awake at the same time (this is akin to the TIGWorld threads, which I personally find appealing from a collaboration perspective).