Update: Instacart is now offering groceries from Whole Foods, and expanding its coverage area to include neighborhoods like Brighton, Jamaica Plain, Brookline, and North Dorchester.

With holiday parties and family meals looming, it's easy to see the appeal of Instacart : you can order groceries online and have them delivered to your doorstep in an hour or two, for a delivery charge of as little as $3.99.

And here's the twist: similar to errand services like Task Rabbit or transportation networks like Lyft, just about anyone who can find their way around the produce section can sign up to earn money as a grocery courier for Instacart. The company says that its "personal shoppers" earn an average of $20 an hour, but they're paid based on the number of orders they handle, and the size of those orders. It raises the interesting possibility of pocketing some extra dough by shopping for a few neighbors whenever you visit the store.

"My fridge was always empty," says Instacart founder and CEO Apoorva Mehta, right. "I just never had time to go to the grocery store during the day." Mehta previously worked to improve order fulfillment at Amazon, and as an engineer at Qualcomm and RIM. Instacart started in San Francisco, and expanded to Chicago in September; Boston is Instacart's third market. "Our goal is to offer an Amazon-like experience without building any the infrastructure, using crowdsourcing," Mehta says.

At first, Instacart will offer only groceries available at Shaw's. But it will eventually expand to offer items from Whole Foods and Costco and other stores, Mehta says, letting consumers purchase certain items from each store, and have them simply materialize on their doorstep a few hours later. Typically, Mehta says, if a consumer chose items from three different stores, that order would be filled by three different personal shoppers. Instacart says the food prices on its site can be the same or higher than the prices you'd pay in the store.

For consumers who request delivery in less than two hours, the company charges a $3.99 fee for orders over $35, and $7.99 for orders under $35. The minimum order is $10. The company says its fastest delivery was made in 19 minutes, but deliveries can also be scheduled for specific times or days when you'll be home. Instacart also offers a service similar to Amazon Prime: for $99 a year, all under two hour deliveries over $35 are free.

The company is in the process of signing a lease for its local office, in Cambridge's Central Square. Mehta tells me Instacart has already hired one person for its Boston operations, and plans to add two more.

The map of Instacart's initial delivery area, in Boston, Cambridge, and Somerville, is below: