For Mac users, Parallels lets you run Windows without rebooting.  You can run Mac OS X and your favourite Windows applications at the same time. You can even drag-and-drop files between desktops!

Not in the Top 100 in 2013

Website Cost Availability Commercial – Free trial Download
2013 2012 2011 2010 2009 2008 2007
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Comments from those who selected Parallels as one of their Top Tools

“Now I can check how web pages look in IE without finding a Windows machine. Its like getting a windows machine for the price of a software program.”  David Parry
“Sometimes I need Windows on my Mac”  Cary Gordon