[Editor's Note: The Feedcache API is no longer available. This profile is maintained for historical and research purposes only.]
From their site: Tucows Feedcache is Quality of Service for RSS. It is designed to make syndication formats more available and more predictable for developers. Tucows Feedcache: Developer Edition provides a web services interface to a user-populated cache of RSS feeds that developers can use and implement in their applications. Tucows initially developed Feedcache for internal use only, but really didn't see any good reason why such an excellent service should be kept under wraps.