If you look at a bunch of cool location-based apps, you’re likely to find Mashery under the hood. Mashery has a software platform that companies (in this case, location-service companies) can use to market, distribute and keep track of their application programming interfaces (APIs), which allow third-party developers to build apps on their services.

APIs let developers combine location information with other data to create “mash-up” apps. The more apps a particular location service has to offer, the more users become engaged with it.

Today, Mashery is announcing that its customers include Quova, Homefinder.com, CityGrid (formerly CitySearch), WeatherBug, and Allmenus. Each of those app platforms makes it simple for developers to use their APIs via Mashery. In turn, third-party app creators will be able to use Mashery and its customers’ platforms to create specialized, location-aware apps.

Location apps have become so popular, it’s no surprise they’re becoming some of Mashery’s most active customers.

Full told, Mashery has more than 50,000 developers using its API management services. Quova used Mashery to create its own developer portal so that third-party developers could take Quova’s platform and create mash-up location apps with it, said Marie Alexander, chief executive of Quova. CityGrid aggregates local content for more than 700,000 advertisers and provides enhanced listings for 18 million businesses. CityGrid uses Mashery to give its developers access to CityGrid’s content and monetization platform.

A typical mash-up app might access your location information from Quova and then get restaurant data from CityGrid. It could then make recommendations to you about restaurants that are nearby.

HomeFinder.com uses Mashery’s API to enable its 130 online newspaper partners to access real estate data from 3.5 million property listings. The newspapers, such as the Chicago Tribune and Miami Herald, can then weave property listings, community data and school statistics into their web sites and their print real estate sections.

WeatherBug, a brand owned by AWS Convergence Technologies, manages a global weather network and is using Mashery to let developers access data collected from satellites, radar, and other sources and then output the data to Google and Bing maps.

Allmenus, which aggregates restaurant menus for online ordering, and its sister site Campusfood will use Mashery to provide Allmenus content to local content partners.

Mashery was founded in 2006. Rivals includeSonoa Systems and 3Scale. Mashery has raised more than $13 million in multiple rounds from Cisco, First Round Capital, Formative Ventures, 406 Ventures, the Accelerator Group, Salesforce.com CEO Marc Benioff, and angels Dave McClure, Roger Ehrenberg and Jeff Stewart. The company has 35 employees.