Massive Rockets, Engines & Parachutes - More Things That SpaceX Abandoned

In its 18 year history SpaceX has developed a lot of concepts on paper which never made it to flight, or, were never made to work. Either way the company has a rich history of projects that seemed like a good idea at the time but fell out of favour due to difficulties with engineering, a dearth of time, or a lack of a customer wanting to pay the cost.