What are some alternatives?
Atlassian Bitbucket Server - Atlassian Bitbucket Server is a scalable collaborative Git solution.
MadCap Flare - Documentation for Any Audience, Language or Format
Visual Studio Team Services - Visual Studio Team Services (VSTS) provides unlimited Git hosting, cloud build for CI, agile planning and continuous delivery.
HelpNDoc - What is HelpNDoc ? Easy to use yet powerful help authoring environment which can generate various documentation formats from a single source.
GitHub Desktop - GitHub Desktop is a seamless way to contribute to projects on GitHub and GitHub Enterprise.
Dr.Explain - Dr.Explain software is a help file authoring tool.