OpenFeint co-founder Peter Relan has launched OpenKit, his new open API service for mobile developers that guarantees no lock-in of developer data. Additionally, Relan revealed that over 500 developers have signed up for the program since it was announced in December and a private beta program is starting today.

The service is designed for mobile developers, both Android and iOS who are interested in using cloud data storage for functions like leaderboards, multiplayer features and in-app purchases in their titles. Developers will also be able to host their own backend service, with the source code being made under Apache and AGPL licenses; Apache will be used for client code and AGPL for server code.

Since it was announced in December, OpenKit have enthusiastically shown support for the API. In a statement, Relan said hundreds of developers signed up for the program as soon as news of the project hit the web. According to Relan, even iOS developers with access to Game Center services are signing up for OpenKit because it’s a single API and service across iOS and Android. As a result, mobile developers like OrangePixel, Flightless Lt, and Massive Finger are signed on.

OpenKit’s private beta program currently involves 50 developers but a public beta of OpenKit 1.0 is expected to go into public beta later this month, followed by a live production in March. Currently, Version 1.0 features cross-platform cloud storage for game save states, cross-platform leaderboards and authentication services for Facebook and Twitter.

When OpenKit was first announced, Relan revealed his motivation was to provide independent developers with an alternative to the “extreme uncertainty” they face regarding their data and users when platforms are acquired (as was the case with OpenFeint). Relan believes there should be an open source cloud service for studios allowing them to take both their code and user data with them if they ever decide to move away from the service.

This is good timing for OpenKit, as GREE recently announced it was shutting down the OpenFeint network and many developers were already looking for an alternative API.

Developers interested in taking part in the private beta and/or who want to contribute to OpenKit’s open source project can register here.