RABL, The Ruby API Templating Language
Inspired while building a public API and by frustrations with JSON generating libraries like tequila and json builder, I have created the RABL templating engine which allows you to define JSON and XML APIs in a clean, simple ruby DSL. a The gem also removes code duplication allowing template partials and inheritance. Works with Rails 2.X, Rails 3.X, Sinatra and Padrino. Benchmarks are forthcoming.