Wikipedia
Postmates is a logistics company which operates a network of couriers who deliver goods locally. Postmates is closely compared to Uber because of its use of mobile phones to receive orders and dispatch delivery drivers. As of December 2014, Postmates operates in 18 U.S. cities. As of October 2015 their website lists more than 100 metropolitan areas.
The service is part of a category of businesses that rely on mobile phone applications and their Global Positioning System capabilities to quickly match inventories and consumer demand. Postmates is an example of an on-demand company. Postmates co-founder Bastian Lehmann calls the company anti- Amazon, saying "Amazon comes along and builds a warehouse outside a city. We like to say the city's our warehouse. We try to understand the inventory available, hacking the city, and having a fleet of delivery people that distribute these inventories."
Postmates.com often gives out promotional codes to entice new customers. Postmates gives out these codes during holidays, season change, cultural events, etc.