A gridnaut is an avatar who crosses over from one virtual world to another. The idea of moving between virtual worlds (not regions) is one used in both AFK and The Day is Full of Birds (probably time for me to start using some new ideas, then). Linden and IBM have been very vocal about their collaboration on a project to enable this, and recently a group of keen researchers made the first teleport from Second Life to another virtual world. Read more about the project here.
Have you got what it takes to become a Gridnaut?