AN ENCYCLOPÆDIA OF PAYWALLS & AN EXPLORATION OF VALUE ONLINE.
Paywall (n.) 1. A barrier erected on the web that requires a user to pay for access to information: The New York Times is putting new articles behind a paywall! 2. A costly misunderstanding of the nature of the web: Can you believe the New York Times is putting new articles behind a paywall? 3. One aspect of my Master's thesis at NYU's Interactive Telecommunications Program: Alex has made a bunch of alternative paywalls.
NB: you used to be able to play with them here, but many years have passed and, unfortunately, the telephony provider he was using went out of business, as did the IP geolocation provider. A change of host wreaked havoc on all his PHP and mySQL databases, so rather than interacting with the individual walls as you used to, you can read about them here.