Abstract: Provided herein are expandable devices, rail systems, and motorized devices. In one embodiment, an expandable device comprises an expandable sac having a tool housed therein. The expandable device is optionally configured for operation while inside a body cavity. The expandable device optionally comprises at least one rail in the sac, and at least one railed device coupled to the rail for movement there on. Movement of the railed device on the rail is provided by, for example, a motor such as an electromagnetic motor or an inch-worm type motor. Expandable devices can be used, for example, to perform minimally invasive medical procedures requiring access to a body cavity. Expandable devices can also be used, for example, to provide safe and stable transport of instruments to the body cavity.