Not really like tesla coils, except in that it's pretty high voltage stuff and sometimes knowlegable geeks make them for fun.
Tesla coils are actually air-cored resonant transformers that produce high voltage, high frequency electricity, and a nifty light show when that electricity starts arcing. Railguns simply use electricity to generate a magnetic field to propell an object.
the guys at
this site have a more recognizeable railgun with some good pics of the completed project.
this is a pic from their site:

on the far end in the background with the blue tubes on the sides, that's the injector. You'd stick the projectile in that end, and it would shoot down the barrel, out the end in the foreground. Electricity flows through bars on either side of the barrel [you can't see them here, they're deep inside the barrel casing]. Electricity produces a magnetic field anytime it flows through a conductor, and since the electricity flows down the one side, and then back up the other [oppisite directions], the magnetic fields are opposing each other. Normally this would make the bars push away from each other, but since they are fixed in place, they can't move away, and that repelling force can be used to push an object between them, away from the power source on the injector end, and out the muzzle.
Archived topic from Iceteks, old topic ID:1553, old post ID:13078