The popular fitness app, RunKeeper Pro, will be available to download for free permanently, according to the app’s developer (FitnessKeeper, Inc.). The application has been rebranded “RunKeeper,” and its free sister app – RunKeeper Free – will no longer be supported.

RunKeeper Pro dropped its price tag ($9.99) on December 30, and the promotion was supposed to last for one month only. However, after receiving a massive number of downloads – more than one million in just four days – the app’s developer has decided to keep the app free.

According to TUAW, FitnessKeeper, Inc. will concentrate on bringing in revenue via subscriptions (such as RunKeeper Elite, which works with both the application and http://runkeeper.com/) and the RunKeeper store.

The application allows Apple fans to monitor their fitness activity via GPS, and syncs data with RunKeeper.com. As mentioned, the app was previously priced at $9.99.

However, users can now grab the app for free – and will be able to do so for the foreseeable future. Check out RunKeeper in the App Store, and let us know your thoughts on the application in the comments.