Part of the Personal computing glossary: A socialbot is a software program that simulates human behavior in automated interactions on social network sites such as Facebook and Twitter. As a rule, socialbots are designed to pass the Turing test: They're sophisticated enough to fool other users and be taken for a human.
Xorg is the default X Window server since Debian 4.0 (etch). It replaces XFree86 and is maintained in Debian by the XStrikeForce.
In the strictest sense, the answer to your question is that the most popular graphical user interface for Linux is X11, specifically the xorg implementation of X11, but there are and have been several other implementations of the same standardized system, also known as X-Windows..