10. Corel and Microsoft

Frenemies since: 1989, when the fledgling, Ottawa-based Corel introduced the first version of CorelDRAW. It was a Windows graphics application at a time when most software developers were on the wild goose chase known as OS/2, and it did as much as any app to establish Windows as a legitimate platform for significant new applications.

Acts of friendship: In 2000, Microsoft invested $135 million in then-struggling Corel in return for Corel’s support for Microsoft’s .Net platform; in 2002, Corel was an early booster of Microsoft’s Tablet PC with its Grafigo application.

Acts of enmity: In the mid- to late-1990s, Corel founder Michael Cowpland bought bought WordPefect from Novell and pitched it as Pepsi to Microsoft Office’s Coke, wrote another Office rival from scratch in Java, attempted to consumerize Linux into a Windows competitor, and frequently bashed Microsoft in public. Cowpland was forced to step down in 2000, and the company then largely abandoned its efforts to turn itself into the Microsoft of the Great White North.

Current state of the frenemyship: WordPerfect is still around, but even Corel markets it more as as a Royal Crown Cola than a Pepsi; the company has gone back to being a solid citizen on the Windows platform, and is no longer trying to kill the king. I’d say this is one frenemyship which blossomed into a friendship–though not, of course, one of equals–period.