Ancient
Ancient is a casual constructed Magic: The Gathering format that only allows cards from the original border sets (Alpha through Onslaught). [1] In contrast to QL Magic, Ancient uses modern rules.
While the card pool is limited, it also allows players to use cards from Magic's past that might be deemed too weak by today's standards - creatures in particular. There are SOME exceptions where cards from a cycle that were printed in a 'Modern' set are allowed, but only when these cards were printed to complete a cycle from an earlier set (most notably, the Zendikar fetchlands that completed the cycle from Onslaught).
Note: reprints from the Alpha-Onslaught sets with new borders are allowed.
At least, that is how it all started out. After a few tournaments, some of the players wanted to capture more of the good old days feeling of the game, and reduced the card pool to Alpha up to Mirage, to get more of a feeling of playing in 1995-1996 era. Today, there is also a website dedicated to the format, which can be found at ancientmtg.com. There you can find some pictures, the rules, and also information as to how the format compares to other eternal formats.