This one is a classic. In 1980, when IBM was looking for somebody to build a disc operating software for its brand-new IBM PC, Microsoft was not its first choice. In fact, none other than Bill Gates suggested that Big Blue approach Gary Kildall of Digital Research, author of the CP/M operating system.

The legend is that Kildall blew IBM off to go fly his plane. The real story is that Kildall was flying to deliver a product to another customer, leaving his wife to negotiate with IBM. and sent the executives packing.

Big Blue went back to Gates, who with his partner Paul Allen whipped out MS-DOS, based on Tim Paterson's QDOS (the Quick and Dirty Operating System), which was itself based on CP/M. IBM ended up offering both Microsoft's DOS (for $60) and a version of CP/M ($240) to buyers of the original IBM PC. The cheaper product won.

Before DOS, Microsoft's biggest products were versions of the BASIC programming tool. After DOS, well...you know the rest. Would Microsoft have grown into the monolith it is today without the IBM contract? We'll never know.