OpenTable is an online reservation service. It lets people find reservations at local restaurants and book them from their computer or mobile phone; all the while, not having to use the traditional system of calling or visiting the restaurants in person.
Along with its reservation system, OpenTable also maintains a database of restaurant information and reviews from both its users and partners. Similar to Yelp and CitySearch, this lets people recommend or discourage restaurants in OpenTable's database. Those reviews show up to other users when they do a search or while they plan to book a reservation.