This site is powered by Open Source. What is open source? It’s software written by folks and made available for use or modification. Open source is free as in freedom. It usually doesn’t cost you anything to obtain it, so it’s often free in that sense. If you count the time it takes to install, configure, learn and use it, it’s not free. You are free to obtain the sources and study it, make changes or whatever….that’s why it’s free as in freedom. You are not restricted in your use of it, unlike many other software products.
I use open source every day in my job, my laptop is powered by open source linux. The blog software is open source, and the server it runs on is open source.