If you love Parse, you'll be happy to hear that the company just released an OS X SDK. Parse helps you store, sync and push data, enabling you to build server-based apps in the cloud without having to bring your own infrastructure.
The new OS X API supports Mountain Lion development and you can check out the iOS/OS X guide for details on how you can store objects, access social media accounts, create "GeoPoints" and provide push notifications. There's a QuickStart guide that helps you get going in Xcode.
Parse offers a free account with up to 1 million pushes per month ($0.07 per 1,000 pushes over that amount) and a "pro" account that supports collaboration, and higher storage and API request calls volumes.
I am not personally a Parse user but it has very good buzz as a service.