Wikimapia is a web service that allows users to edit information on a world map in a wiki format. Users of the site can add places, edit them, and get the information previous users have entered. The info there is currently pretty sparse, but the service is rather new. The company also recently released a Wikimapia API that supports getting information from the web service.
The press release describes the API:
We've been promising this since the beginning, and now it happened. Today we open our Wikimapia Database through Wikimapia API. Since that day developers around the world can integrate Wikimapia Geo Data into their external applications and web sites. We provide you with free access to Wikimapia DB, collected by our contributors, with the aim to help the geographic community to use this data not only on Wikimapia site, but through any other website or application, including mobile and GIS apps. So everyone can use them everywhere.
We open Wikimapia data free for non-commercial use (as you mention the original data source, according Wikimapia TOS). We will be in close contact with developers via our discussion forum in API section, supporting them with all the required documentation and updates. Hope soon we will publish a best-practices guide for our API. Our API is still a developing stage (beta), more features will be added soon such as roads, graphic tiles use, then adding information from mobile devices to Wikimapia DB.
The API is still currently sparse, although it shows a lot of promise. All that's available is info on places within a defined box, and info about a specific place. Inputting new data is currently not covered by the API. It is a RESTful service, and requires an API key (easy and free to make). It outputs data in a surprisingly robust set of formats, including xml, kml, json, jsonp, and a unique binary format, as well as offering output gzipped if data volume is a problem for you. You can choose whatever format you want, gzipped or no.