API documentation tool: If you have a REST(ish) API, the tool would allow you to:

* Describe the authentication

* Enter all the objects, methods, URL endpoints, and parameters of your API

The tool would then:

* Generate pretty documentation, including example requests/responses

* Include a working web-based API console (like Mashery has)

* Auto-generates client libraries in Ruby, Python, PHP, Node, Obj-C, etc. and keep them updated in GitHub

Bonus points for bootstrapping the API information from your Rails routes file.