While the InformationWeek article does talk about Unix/Linux in general as the top entry of its 12 greatest software programs of all time, it singles out BSD4.3 as the heart of the system's greatness and global significance.

The full article, with explanations for all the choices, is available at InformationWeek's website, but here's the list.

1. Unix/Linux (and specifically BSD4.3)
   
2. IBM's System R (the first DBMS)
   
3. The Human Genome Project
   
4. IBM System 360 OS
   
5. Java language
   
6. Mosaic browser
   
7. Sabre system (airline reservations)
   
8. Macintosh OS
   
9. Excel spreadsheet
   
10. Apollo guidance system
    
11. Google search rank
    
12. The Morris worm
    

The author, struck by guilt over not inclusing MS-Windows felt compelled to give an explicit explanation of why not.