Stickybits is an iPhone app that talks to barcode stickers, allowing you to program messages and stick them to physical objects. You can buy a pack of 20 for around 10USD, but you can also download and print your own barcodes for free. "Each barcode is programmable by the first person who scans it and and leaves a photo, video, audio, or text message. The next time somebody scans that barcode, the previous message will appear on their phone. Anyone can add a new message to the same code, resulting in a stream of messages connected to whatever object or place the barcode is stuck on. Each scan, and related message, is geo-tagged so you can see as an object moves around how its story evolves."