Apple, the most successful smartphone company in the world, was founded in 1976 by Steve Jobs, Steve Wozniak, and Ronald Wayne. The company's first product was the Apple I, a personal computer hand-built by Woz and sold in part-completed kit form. The Lisa was replaced by the Macintosh in 1984, which transformed the world's understanding of what a computer is. However, Steve Jobs and John Scully fell out in 1985 when Steve wanted to focus on the Macintosh, leading to an increase in product sales. Despite this, Apple was in trouble in 1996 and Steve was brought back in 1997 to develop the NeXT operating system, which is now the basis for Mac OS X. Apple's product lineup includes five different Mac families, four iPad ranges, and several Apple Watch models.