The Gaussian Linear Accelerator project takes me back to high school, and is of special significance to me because it was one of my first builds. The idea was to take a popular science fair toy, namely the Gauss rifle (a permanent magnet version of a coilgun), and design it with a raking mechanism to retrieve ("reload") the steel balls used in its configuration to transfer kinetic energy. This would effectively make the device pump-action, a vast improvement over manual reset after the projectile has been released. The design was submitted to the 2011 Google Science Fair (See here), and after finishing the build, I had a lot of fun testing my world class peashooter on my unsuspecting friends!