ReadMe provides an easy-to-use solution for creating API documents. With its API explorer, let users play with your API right inside the documentation. Keep everyone up to date with what's going on via announcements. Markdown-based drag-and-drop editor makes documentation almost fun. Easily create a beautiful dev community that matches your brand. Let users ask questions and request features in the support forums. Maintaining old or testing beta versions of your docs is a breeze. ReadMe isn't just for public docs! It's easy to set up internal documentation.
Gelato was recently acquired by Mashape and is available as an on-premise option as well as a SaaS offering. It is free to use for open-source projects and has an Enterprise edition available for large scale applications. Pricing for Enterprise edition hasn't been disclosed by Gelato.
API Documentation Solutions Gelato