Structured data has an open platform, thanks to a new startup aptly named Factual. At first glance, it seems like Excel on the web. However, Factual is more database-oriented, with joining and filtering built-in. Plus, sharing and discussing the data is an integral part of the experience. Most functions on the site, including both reading and writing data, can also happen via the Factual API.
Once you get beyond the most basic map mashups, you'll run into a problem with data storage and access, because you can't hard-code hundreds of markers. It's a problem that SimpleGeo wants to fix. And from the looks of their new platform, they've gone beyond expectations.