TechCrunch reports that Boxcar, developer of the popular Push Notification app of the same name has implemented a new Provider API to allow third-party services to leverage its Push Notification service. Previously Boxcar provided Push Notifications for specific services such as Twitter, Facebook and e-mail as well as a user API for individual users to customize their own Push Notifications from desktop apps such as Growl. The new Provider API allows web sites and other online services to build their own customized Push Notification feeds that can be subscribed to by any Boxcar user. Boxcar plans to allow third-party providers the option of charging for their Push Notifications via a one-time in-app purchase with revenue shared 50/50 between Boxcar and the Provider. Boxcar is available from the App Store as a free download and includes Push Notifications for one service; additional services can be added via in-app purchase for $1 each.