LMFAO. You must be joking. This is the most inaccurate statement I've heard in a while... Open source stuff is usually better than the commercial competitor unless you're talking about huge volume mainstream (like MS Office).
Firefox or Chrome > Internet Explorer
7-zip >> WinZip or WinRAR
Filezilla > commercial FTP clients
Audacity > bundled audio editors
CDBurnerXP > bloated NERO or Roxio
FoxIt > Adobe's own reader
Pidgin > AIM
gnuCash > Quicken / MS Money
Plus how can you live without AdBlock, Peerblock and Speedfan? All my small utilities, and
all my security stuff is also open source.
The majority of the internet runs on Apache running on Linux/BSD boxes with Snort IDS and IPFW or IPTables protecting them and using OpenSSL to secure their connections. The majority of the email on the web goes through Sendmail, Postfix or Exim.
I'd even go so far as to say that linux is better than Windows for specific needs (not generic consumers, gamers, office work). For specific apps though, like dedicated firewalls, web servers or network file servers, etc., it can't be beat.
BTW - the guys that worked on Open Office before Sun shafted the project went on to create LibreOffice.
http://en.wikipedia.org/wiki/LibreOffice
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For my use, the only thing I can't replace with open source is Quickbooks & Solid-Works + games at home. Though I will concede that Office is better than Open Office, it is not $250 better.