Fallout is a 1997 role-playing game by Interplay that was originally intended to be a sequel to Wasteland. However, because Interplay did not have the rights to the title, Fallout was eventually set in a different post-nuclear world, albeit with many references to Wasteland. Fallout went on to have sequels and spin-offs of its own. Developers of Fallout games included Chris Avellone and Mark Morgan, who went on to work on Wasteland 2 as well.
For more information see The Vault.