Other than the OS/2 that is the base of my web server, everything is basically "Open Source". If you want a better definition, take a look at OpenSource.org. This is software that is in the public domain, written usually by a team of software developers. It is also a swipe at that giant in Redmond, Washington who does not take kindly to working with others – read "Microsoft."
This is not to say that I don't use any MS software, but rather that there is better software that "works well with others." MS even came out with their "Open XML", and then made it different so that is won't work with "Standard" XML. Yes, there are standards in the computer world, and it's interesting how a giant flaunts the standards. Well, so be it! Maybe not in America yet, but foreign countries are passing laws that some MS software cannot be used in their government offices or businesses until they pass the "Open" standard.