Per provider, this API is now closed and API keys are no longer being distributed. Users of the API before it was closed continue to have access to the API but that is not being fully supported
Yipit provides aggregated online coupons, combining the offers provided by over 250 coupon services, including Groupon and LivingSocial. The Yipit API is currently in closed beta, though developers can express interest by filling out the form. No public documentation is available at this time.