6. Microsoft and Sun

Frenemies since: At least 1993, when Microsoft released Windows NT, the first version of Windows designed to compete against UNIXes such as Sun’s Solaris.

Acts of friendship: In 2004, the two companies signed a sweeping cooperation agreement that settled old lawsuits, put over a billion dollars of Microsoft money into Sun’s coffers, and involved collaboration on multiple technical fronts. Today, Sun is a Microsoft Gold Certified Partner that certifies its X64 servers for use with Windows.

Acts of enmity: The two companies’ rapprochement was stunning given that for years, former Sun CEO Scott McNealy (at left in photo, making nice with Steve Ballmer) was the industry’s most high-energy Microsoft basher, calling Windows a “hairball,” .NET “.NOT,” and Outlook “Lookout.” At COMDEX 1999, he declared that the company’s free StarOffice rendered Microsoft Office obsolete, called for the breakup of Microsoft, and even hired magicians to turn a copy of Windows into a Monopoly game.

Current state of the frenemyship: You kinda wonder whether that 2004 agreement included a top-secret clause prohibiting McNealy (who stepped down in 2006) from sniping at Microsoft. If today’s kinder, gentler, smaller Sun is still stewing about the inroads Microsoft has made on its former cash cows, it keeps its discontent to itself.

(Photo of Scott McNealy and Steve Ballmer from Microsoft)