* Linux, FreeBSD, NetBSD, OpenBSD, Solaris, Microsoft Windows
* POSIX, C89, C99, C++, Java
* the World Wide Web
* the GPL and the FSF
X was one of the first major open source software projects, years before the terms Free Software and Open Source Software were commonplace. Celebrate with us, for without X, the desktop would not be what it is today.
Ping.
I've read some really good screeds against X over the years, but ultimately it all boils down to a very simple question: does it work, nor not?
Overall, I'd say that it has held up rather well over the years. You can do a lot of really cool things with X, working through tunnels (ssh of course). I used to occasionally open up Firefox (or whatever it was called that week) remotely using SSH to test how a website looked from outside a corporate firewall. It was cool, secure and useful. Biggest drawback was speed, but that wasn't my primary concern at the time. X still has speed issues but there is a lot you can do to optimize things. I still think it is cool that I can open up a gui application on a computer on the other side of the planet, and aside from responsiveness, not have any real issues at all.