Ubercart has included the Recurring Fees module as a core module for some time now, allowing users to associate recurring fees with products that customers must pay for via credit card. Unfortunately, the module was never really there in terms of practical uses and extensibility. Due to its limitations and to its relatively minor importance to the Ubercart project as a whole, the development team decided to move it into contrib space where it could mature without limiting or being limited by the core Ubercart development cycle.
UC Recurring Fees 6.x-1.0 is a straight migration of the code from Ubercart as it stood at its latest point in the 2.x development cycle. It was removed between RC1 and RC2, as we forgot to nail down the issue prior to tagging the 6.x-2.0-rc1 release. Several community members have been developing code and ideas to greatly improve and maintain this module, and they will work on it through this contrib in the 6.x-2.x version and beyond.