What is reality? If that question garnered a Keanu Reeves-like "Whoa" from you instead of an eye roll, you're in the right place. Alternate-reality stories have become one of the most prominent subgenres of science fiction over the past century. This spilled over into Hollywood in the late 1990s, with one particular film in the genre (The Matrix) becoming one of the most influential action films in the history of cinema.
But the Wachowskis' classic is just the tip of the iceberg. Famous directors like John Carpenter and David Cronenberg have taken stabs at alternate-reality films, and movies like Dark City and The Congress deserve to be seen by many, many more people. If you're cool with spoilers, scroll on down and get ready to question your existence - and don't forget to vote up your favorite movies that, true to form, may or may not be real.