Fallout franchise started in a very different way than we all know it by this day. As Bethesda started to develop Fallout franchise only from the third game, original Fallout was completely different.
The game starts in 2161, 84 years after a nuclear war destroyed most of the planet and turned into Wasteland. You can either create your protagonist or play as three pre-set options - Albert Cole, Max Stone or Natalia Dubrovhsky. When in Vault 13 water supplies start to malfunction via technical reasons, Overseer sends protagonist in a quest to find a replacement and save the Vault. Having Pip-Boy and some standard equipment, the Fallout world is absolutely open for exploration.
Although being a completely different genre of the game, Fallout still uses the same systems as we know today. S.P.E.C.I.A.L. system of characters stats (strength, perception, endurance, charisma, intelligence, agility and luck) affect your skills in a variety from 0% to 200%, as well as definitive straits that you choose only once for whole gameplay. Known to players as Karma, you can choose how to act in most of the situations and determine your reputation with other characters in the game.