At Willowtree, we created Monkeypod (https://Monkeypod.io https://Monkeypod.io) to serve as an API design, documentation and virtualization tool. It uses Swagg

At Willowtree, we created Monkeypod (https://Monkeypod.io https://Monkeypod.io) to serve as an API design, documentation and virtualization tool. It uses Swagger and swagger ui extensively and can output (and soon input) Swagger specs. It creates a virtual API based on the design you create, and you can play with it from Swagger ui sandbox or any Http client. We have a lot of cool features on the roadmap. Feel free to sign up and give it a try. Let us know what features you'd like to see. Cheers!