4. Microsoft and Windows developers

Frenemies since: 1985, when Microsoft released Windows, which eventually became the planet’s dominant software platform.

Acts of friendship: Microsoft provided major software developers such as Ashton-Tate, Borland, Lotus, SPC, and Symantec with the platform they wrote most of their software for; software developers provided Microsoft with most of the applications that made Windows useful.

Acts of enmity: At the same time, Microsoft entered most of the major application categories where third-party developers thrived, eventually driving most of them into irrelevance. (When was the last time you powered up Lotus 1-2-3, dBASE, or Harvard Graphics?) Its bulldozing of the competition prompted plenty of grumbling and charges that it enjoyed an unfair advantage given that its application developers and operating-system developers were all one big happy family.

Current state of the frenemyship: Ashton-Tate? Dead. Borland? No longer publishing desktop apps. Lotus? Ditto. SPC? Dead. Symantec? Still a major Windows developer, but not a particularly happy camper. And Microsoft? By far the largest developer of software for its own operating system, thank you very much.