What are some alternatives?
When comparing GitBook and Swagger UI, you can also consider the following products
Atlassian Bitbucket Server - Atlassian Bitbucket Server is a scalable collaborative Git solution.
ReadMe - A collaborative developer hub for your API or code.
Visual Studio Team Services - Visual Studio Team Services (VSTS) provides unlimited Git hosting, cloud build for CI, agile planning and continuous delivery.
ReadTheDocs - Spend your time on writing high quality documentation, not on the tools to make your documentation work.
GitHub Desktop - GitHub Desktop is a seamless way to contribute to projects on GitHub and GitHub Enterprise.
Apiary - Collaborative design, instant API mock, generated documentation, integrated code samples, debugging and automated testing