14.4 has plugin support (and there are a load of excellent plugin add-ons already; solar panels that generate energy, an energy-based fuel system, auto-orienting satellites, an autopilot, blimps, lasers that track other objects and overheat them to the point of combustion, extendable landing gear for spaceplanes and rockets, functional carts/rovers, robotic servo-motors that rotate attached objects, who knows how much I\'m omitting), a new terrain generator for Kerbin as well as the Mun, persistence and the tracking station (begin any mission where you left off; rendevous with previously launched craft in orbit or on the Mun, et cetera), as well as access to all future versions of course. 0.15, coming out very soon, will have a horizontal hangar for spaceplanes, official spaceplane parts that behave very differently and much more sophisticated than the current ones, and an improved runway, amongst other features. You\'re also getting it for much cheaper than it will be in the future and helping fund additional development of the game.