The Rally .NET SDK by Joshua Stupplebeen interacts with the API, even though Rally Software does not maintain the kit actively. User guide provides links to access REST API and Web Services documentation. For support, ask a question at http://stackoverflow.com/questions/ask?tags=rally
Business applications created on the Cloudfier platform inherently contain an API that grants full access to app functionality through the Cloudfier API. Cloudfier allows users to define a business centric solution with Cloudfier’s business programming language. After the solution is defined, the platform automatically creates a web application. Cloudfier was built on Elipse Orion and aims to move towards a new type of development.