This wasn't technically an acquisition, but it wasn't Microsoft home brew, either. SQL Server was a Sybase product that ran on Unix. The company teamed with Microsoft and Ashton-Tate in 1989, maker of the once-dominant dBASE database software to port SQL Server to OS/2, back when Microsoft was still an OS/2 supporter. Ashton-Tate dropped out, and in 1992, Microsoft and Sybase ported SQL Server to Windows NT. The two companies split in 1994, with Microsoft taking sole development lead. But it hadn't gotten rid of all of the Sybase code until SQL Server 2005 came out. Now Microsoft SQL Server is a major competitor to Oracle, and Sybase has all but vanished as a significant RDBMS vendor.