I have been using Linux for about three years now. It started started when I went searching for a free or shareware piece of software to solve a particular problem I was having with Microsoft Windows, and I stumbled across this whole community that I had never before heard of. That is the Linux OS and Open source software community.
This is actually a cluster of communities, because there is free and open source software available for every operating system and computer platform that exists. However, I was particularly drawn to the Linux community, because here, even the operating system is free.
Here, I feel I must qualify what the community means by the word "free." Most people see that word and immediately think, "Awesome! I don't need to pay anything for this great software!" However, that may or not be the case. Certainly, a lot of the open source software is provided at no initial cost to the user, but the community defines freedom differently. They intend you to understand that the software is free to adapt, modify, distribute.
The beauty of this is that many software developers, hackers, coders, programers, etc., take it upon themselves to improve and grow baby software projects until they are full-featured, and useful for everyone.
The other result is that the communities keep growing like a snowball rolling downhill. There are, today, thousands upon thousands of free and open source software packages that you can choose from to meet your every software need!
You can find a lot more information about free and open source software on sites like:
http://www.ubuntu.com
http://sourceforge.net
http://freshmeat.net
http://distrowatch.com
http://www.freesoftwaremagazine.com
And be sure to check out all of the links on those sites!