You start with a picture and post pics that visually rhyme. Based on whatever you see fit. Of course, you can invite friends, too! Over time a stream of association emerges, the "verse"
The frontpage is at http://picrhyme.com/ and a good example of what happens can be found here: http://picrhyme.com/images/180/history (How to get from Helvetica to Asparagus via Woodstock!)
At least for me it triggers some really ticklish place in my brain, adding those picture rhymes. Maybe you'll enjoy it as much as I do.
Thank you for any feedback and with best wishes.