Sushimako, my YC cofounder actually reminded me of some more details:

Here's a video [0] of Bre Pettis talking with Michi about Laser Tagging from the Graffiti Research Lab in Austria [1].

And the app by Michi and oneup (my other YC cofounder!) was written in Processing.

[0] https://youtu.be/isfrCIhQ5HE [1] https://graffitiresearchlab.at