coilgun
One of my earliest electronic creations, it's a coilgun fabricated from several disposable cameras, some wire, a magnet, a pen, and some electrical tape. I found it sitting in a drawer while cleaning; uploaded for historical note and personal amusement.
Instructions for assembly were (and still are) readily found on the web. The magnet is to be taped to the end of the pen to hold the projectile in position before firing. Range is approximately 15 feet, which was disappointing to my 14 year old self. I distinctly recall zapping myself (somewhere around 300V) only once during the process of assembly and testing.