Build prototype onto our open API

Our classified site is for Latin America and available in 3 languages. It has over 7 million pageviews per month. We want to develop an external tool that uses our open API. The purpose of this tool is to be able (when granted access) to upload and then edit and delete ads on mass for our large scale users, such as real estate, used car dealers, or any site with large data sets appropriate to a classified site. In this tool the user will be able to create, update or delete their ads in batch, perhaps processing CSV files or XML. We accept suggestions for features and improvements in our API as well. Development must be done using Ruby on Rails and the use of tests with test / unit and rspec is mandatory.