#4 - SCO

Once a prosperous, medium-sized software company, the Santa Cruz Operation (SCO) began its fall shortly after being acquired by Caldera, Inc.

The incoming CEO and former CEO of Caldera Ransom Love wanted to merge Caldera and SCO's Linux and UNIX product lines, and create a best of breed OS.

This didn’t work and SCO's sales of UNIX products went down and it was forced to lay off virtually all of its employees to focus entirely on many lawsuits it faced with its competitors.

#3 - AOL

Facing challenges from the growing Internet and broadband industry in the late 1990s, on-line services provider America Online pursued a strategy of re-invention as a content and broadband giant by purchasing Time Warner in the year 2000 for a whopping $164 billion.

It turned out to be a total failure, with the new company unable to capitalize on Time Warner's strengths. Total subscribers of AOL went from 30 million to just over 5 million in 2007, with no significant quarterly growth since 2002.

In 2009 AOL announced it would spin off Time Warner into a separate public company, ending a fruitless eight year relationship.