Date: July 27, 1981

Acquired for: $75,000

In a last-minute effort to deliver IBM a 16-bit OS for its personal line of computers, Bill Gates and Paul Allen bought QDOS (AKA 86-DOS) from Seattle Computer Products for a meager $25,000. Soon after, the duo hired SCP programmer Tim Paterson and dropped an extra $50,000 for all rights to 86-DOS—opening the lane for Microsoft to license its own PC software, which would become Windows. The rest is history.