How it works: San Francisco-based Postmates, an on-demand delivery startup, offers restaurant delivery in an hour or less via smartphone app. It typically charges a delivery fee, which starts at $5, and a 9-percent service fee that is applied to the purchase price.

Postmates' Pop service, which promises delivery in 15 minutes or less, is available in San Francisco, Los Angeles and New York.

Who it caters to: Postmates operates in more than 20 states and the District of Columbia.

Notable partners: Postmates, while not exclusive to restaurants, has signed big names such as Chipotle Mexican Grill, McDonald’s and Starbucks, pictured here.

How it works: DoorDash has emerged as one of the top players in the third-party restaurant delivery space. The on-demand service promises delivery in 45 minutes or less, but not always with the explicit permission of the restaurant chain.

Related: Taco Bell faces growing pains with delivery

Who it caters to: DoorDash is available in 24 major metro markets across the U.S. and Canada. Some of these include Atlanta, Seattle, Chicago, parts of New York City, Phoenix, San Diego and Dallas.

Notable partners: DoorDash works with more than 1,000 restaurant chains of two or more units. Some of its larger partners include KFC, Dunkin' Donuts, Carl's Jr., The Cheesecake Factory, California Pizza Kitchen and Veggie Grill. 

Taco Bell, pictured here, launched delivery service with DoorDash in July 2015, at more than 200 restaurants in California and Dallas. The quick-service operator aims to offer delivery nationwide, potentially in every city where Taco Bell and DoorDash operate.

How it works: Global online retail giant Amazon added restaurant delivery to its Prime Now app in September 2015. The service allows Prime Now users to order from restaurants via desktop or mobile app.

Who it caters to: The service has rolled out in Seattle; Portland, Ore.; Baltimore; Los Angeles; Austin; Texas; Chicago; and San Diego, with designs for nationwide expansion.

Notable partners: Amazon has targeted smaller, local players. For instance, in Seattle it offers delivery for the restaurants Wild Ginger, Cactus, Skillet, Marination Station and others.

How it works: Baltimore-based OrderUp was founded in 2009 and offers on-demand restaurant delivery via desktop, smartphone or Apple Watch for quick-service and independent restaurants. In July 2015, it was acquired by Groupon, but will continue to operate as a standalone brand.

Who it caters to: OrderUp is available in 23 states, typically in smaller cities such as Charlottesville, Va., Santa Barbara, Calif., and Boulder, Colo.

Notable partners: Chains like six-unit Fat Jack’s Supersubs in Denver, which does about 50 percent of sales in delivery with an in-house crew, use OrderUp. The restaurant’s listing on the service offers digital marketing and ordering and payment aspects that the family-operated business wouldn’t otherwise be able to provide, the company said.

How it works: UberRush is an on-demand delivery service by taxi disruptor Uber. The service connects users with couriers to make deliveries of a variety of items, including restaurant meals.

Who it caters to: UberRush offers its services in major North American cities such as New York, Los Angeles, Chicago and Toronto.

Notable partners: Chef and restaurateur David Chang, pictured above, is planning a new food delivery service in New York City called Ando, with delivery provided by UberRush.

How it works: Grubhub offers a digital marketplace for restaurant delivery, but only brings food from point A to point B in select markets. GrubHub is reporting $175 million in annual food sales through its portfolio, which includes Seamless and AllMenus, MenuPages, Restaurants on the Run, DiningIn and Delivered Dish, according to analyst Christopher O’Cull of KeyBanc Capital Markets

Who it caters to: Grubhub is available in nearly 50 markets across the country, including major cities such as San Francisco, New York, Las Vegas and San Diego.

Notable partners: In April, Grubhub announced a partnership with California Pizza Kitchen to process online ordering and delivery services for 117 of the chain’s nearly 300 locations. For 81 of those restaurants, Grubhub will also provide last-mile delivery, bringing food from restaurant to home or office.