John Sylvan invented the single serve Keurig coffee maker in early 1990s. Before the end of the decade, he sold out to investors for a mere $50,000. The company now has annual revenues in the billions of dollars.
Interestingly, the original concept and first machines were intended for offices where employees could create a fresh cup of coffee instead of relying on a full pot coffee maker which often got stale. When they finally developed a less expensive home version, sales really took off.