GNU/Linux
GNU/Linux is a free, open-source operating system (similar in many ways to Microsoft Windows) which is being developed by a diverse team of programmers on the Internet from all over the world. Linux is the kernel (the core of an operating system which allows your computer to read from a floppy, take keyboard input, output text to a monitor, etc.), but most of the basic OS tools come from the GNU project; hence the name GNU/Linux.
This site is being served by a dedicated, Linux-based, web server, which I'm currently administering. My software solution stack consists of: CentOS Linux, LightTPD, PHP, MySQL, Postfix (w/ Spamassassin), Dovecot POP/IMAP, vsftpd, and MaraDNS. While I mostly run Linux for server environments, I'm excited to see its usability as a desktop platform improve in the upcoming years.