Target, Amazon.com, Electronickits.com and ScientificsOnline.com are some places that have electronic kits for building things available, as of 2015. These retailers have multipurpose kits available with projects for building many types of electrical circuits as well as those that produce a finished piece of electrical equipment or toy.
Target has electrical kits available to build remote controlled cars, rovers, motion sensors and robots. Amazon.com has kits for solar powered robots and rovers. ScientificsOnline has a radio building kit and kits with multiple experiments. More sophisticated kits and expensive kits for older kids and adults are available from ElectronicsKits.com, including those for building quad helicopters, electricity generating wind turbines and highly advanced humanoid robots.