Stateful is a game state management and input library for MonoGame and XNA. It grew out of my frustration with the Game State Management sample that everybody and their brother was using in their XNA projects, and when I started to move towards using MonoGame, I brought it along with me.
Stateful is licensed under the ISC license, under LICENSE.md in this repo.
Contact: Ed Ropple (ed+stateful@edropple.com)
Currently, Stateful is essentially feature-complete for XNA on Windows and MonoGame on Windows only. It shouldn't be too hard to create MacOS and Linux ports on a similar basis; similar code should work for the 360 if you want to build a project for it.
Eventually (read: when I need it), I'll be adding gesture and touch support for MonoGame. That should probably work with XNA on Windows Phone 7, too, but I don't have any interest in supporting that.
Stateful is a pretty simple core library--just about anybody could do what I've done here, it's nothing special. (The reason I open-sourced it was in part to encourage myself to write more modular code, which at times flies in the face of established practice in the XNA and MonoGame communities--but that's another story.) There are only a couple of parts you really need to concern yourself with: IInputEventer, StateManager, and Controller.
IInputManager is an interface that defines the input events to which StateManager subscribes (the events of which it delegates execution to the Controllers). You can implement this yourself in whatever manner you'd like, but there's already a DesktopInputManager available under MonoGame. It's a simple polling object and using it will require you to insert a call to the DesktopInputManager.Update() method into your game loop before any calls to StateManager.
StateManager wrangles the various controllers that you'll use to express segments of game logic. It's modeled after a stack, and you use push and pop operations upon it. StateManager includes a small number of events that you can hook for custom behavior; they're documented in-code. Of particular note should be OnEmpty, which will be called when you pop your last controller. Stateful won't close down your application after this - that's still your job. If you don't implement OnEmpty, it'll throw StatefulExitException. If you don't catch that, your application will crash and look dumb. Don't look dumb: implement OnEmpty.
Controller is the unit of state for the project. It's an abstract class with a number of hopefully-obvious implementation members; the required ones can almost all be just left blank at your discretion, but that would make for a pretty lame game.