A cool use of GML by Golan Levin and Jeremy Ficca, called Robotagger:

GML (Graffiti Markup Language) drawings from 000000book.com are converted into DXF via a small Processing utility. Motion paths for a robot arm are planned from this DXF using Rhino and MasterCam. The ABB 4400 series arm is wielding a 2″ Montana Hardcore marker.

[Thanks, Jamie!]

More:

• Graffiti Markup Language week at Fatlab
• Fat Tag Graffiti iPhone app