EverQuest. Although there's nothing in the rules of most games against one player controlling multiple characters, there are usually rules against automating gameplay. This includes sending keystrokes and mouse commands from one computer to several clients, the preferred method for multi-boxers to control multiple game clients simultaneously.
After a hit from the banhammer for "macro use", EVE Online player Zhek Kromtor engineered a low-tech solution to his rule-breaking problem. With a setup that looks like something out of The Matrix or Minority Report, Zhek has set up eight monitors and eight computers to run a total of fourteen EVE clients simultaneously. To control them all at the same time without rule-breaking macro software, Zhek has tied together six computer mice with packing tape and wooden skewers. Six separate keypads have been taped together, with yet more wooden rods letting him activate the modules on six ships at a time. According to the EVE EULA, using software to send keystrokes isn't allowed but there's nothing about taping together keyboards and mice. Whether you think this kind of setup is awesome or a blatant flaunting of the rules, putting together this kind of setup is definitely a bizarre achievement.