http://www.cityam.com/1415624433/mastercard-fare-free-friday-free-travel-londoners-14-and-28-november-using-contactless

Friday 14 and Friday 28 November, part of Mastercard's ongoing
"Priceless London" promotional exercise.

Those looking to exploit this to the full should note that contactless
cards don't work 'Oyster-style' (tap-in etc) on the cable car or on
river buses, nor does it work on the 15H Heritage Routemaster buses.

But Watford Junction, Broxbourne, Shenfield and Grays - as stations
outside the zones but in what was once given the unofficial moniker
'Oyster-land' (now 'Oyster & contactless land'?) - are some of the
exotic destinations one can reach gratis courtesy of the card with the
Venn diagram.

Alas, I'm 'with' Visa (which payment network a debit or credit card is
with is not something that exercises me a great deal!)