A virus is a microscopic organism that can replicate only inside the cells of a host organism. Most viruses are so tiny they are only observable with at least a conventional optical microscope.
Recognized by the Guiness Book of World Records as the MMO with the longest play time per player, and easily the oldest game on this list (launching four years ahead of World of Warcraft, way back in 2001), Runescape deserves mention because it's one of the most updated and popular games of any kind on the planet.
Jack Rabbit may not be the oldest roller coaster in the world, but it is one of the oldest continuously running roller coasters, since it has never been closed for non-operation. When it first opened, it was considered the fastest roller coaster in the world, and it has a 75-foot drop and is 2150 feet long.