While alternate RSS services have started popping up left and right in the wake of Google Reader’s death sentence, the strongest contender so far is certainly Feedly. In a few months, the service already has 12 million users and a pretty sophisticated platform.

Today Feedly officially turned on its own cloud sync, effectively cutting ties from Google Reader for good. The web app has also been redesigned to adapt to multiple browsers on different screen sizes without the need for a plugin.

Feedly had previously been using Google Reader’s backend to sync RSS feeds while allowing existing Reader users to import their feeds. Now that Google Reader’s days are coming to a close, Feedly has fully transitioned to its own proprietary sync technology on mobile and desktop. Google Reader users can still quickly import their feeds when signing up for a Feedly account.

Developers can now use the Feedly API to build the service into their RSS clients. Apps that have announced partnerships with Feedly include Sprout Social, gReader for Android, Press for Android, and Newsify. Popular iOS and Mac app Reeder recently announced that Feedly integration is coming in a future update.

The web interface for Feedly has been redesigned to operate on its own without the need for a browser plugin. You can login into Feedly from any web browser and view your feeds in a clean, app-like interface. The cross-platform nature of the service makes it a compelling option.

Google Reader will shut down on July 1st. We’ll have a roundup of some good alternatives next week. In the meantime, check out Feedly.

• SourceFeedly