When I started Gamefic, my goal was to develop a highly customizable framework for adventure games. It's primarily designed for parser-based interactive fiction, like Inform or Quest. Unlike most other IF tools, however, I wanted Gamefic to be customizable from top to bottom: not just the game code itself, but the clients and the environments that interpret the games:

• Text-based games can be parser-based or CYOA.
• Clients can support images and other media.
• Graphical clients can provide a point-and-click interface.
• Games can run in real-time instead of being turn-based.
• Game code can be interpreted on a server for multiplayer games and MUDs.

[Bla bla. Anyway I'm using Ruby. Now about sandboxes...]