Wikipedia
Caffenol
Caffenol is a photographic alternative process whereby phenols, sodium carbonate and optionally Vitamin C are used in aqueous solution as a film and print photographic developer.
Other basic (as opposed to acidic) chemicals can be used in place of sodium carbonate, however sodium carbonate is the most common.
There are many formulas for caffenol. All are based on preparations which contain caffeic acid (i.e. coffee or tea) and a pH modifier, most often sodium carbonate. The chemistry of caffenol developers is based on the action of the reducing agent caffeic acid (which is chemically unrelated to caffeine).