Postmates API enables businesses to integrate on-demand local delivery into their applications, allowing a wide variety of goods beyond food to be delivered within an hour. The API's appeal lies in its tangible impact, facilitating over 1.5 million deliveries per month, and allowing developers to witness real-world interactions through their code. It supports small businesses by offering distance-based pricing without surge costs, differentiating it from competitors like Uber's delivery API, which focuses more on curbside services. With Postmates, merchants can provide a door-to-door delivery service, enhancing customer convenience. Notable integrations include Shopify, which supports over 20,000 small businesses with delivery options, Spoil.io, which sends local treats, and MeUndies, delivering essentials like underwear on demand. The API's flexibility and focus on local merchants make it a valuable tool for businesses looking to offer immediate delivery services.