For my reference, here’s a list of the various virtual graf systems that I’ve found:
1. Geonotes. Web site is down, and the program failed to connect to the server. This is/was a project based out of Stockholm, but it was the only international system that I’m aware of. It stored messages on wifi hubs, and if I remember correctly, had software out for win2k/XP, Linux, and some obscure PDA OS. I once left a note at Thee Aurafice. Info and screenshots.
2. Tag and Scan a new UK only system. Commercial.
3. Virtual Helsinki: Slashdot discussion
4. FLIRT, also in Helsinki, Financial Times article
5. Urban Tapestries London only, I think
6. Wave Market Global? (Howard Rheingold reviews it here)
Anyone know any others? Seems like there’s something in Tokyo I’m forgetting.