It depends on so many factors, such as the company, open source or not, the scale, the range of products, size of the doc team, whether you want developer/API a

It depends on so many factors, such as the company, open source or not, the scale, the range of products, size of the doc team, whether you want developer/API and user documentation. It also depends how you define user! You could use something like GitHub markdown/GitHub pages. You could use something like Markdown and a custom script like I do for my website (source code in my GitHub). There are solutions like Sphinx (as used by Python) or Jekyll for building a static docs site. You could also use Hugo static site generator etc. etc. - there are many tools out there. These are simple solutions but it ranges up to heavy weight tools like DITA/DocBook (not that I am recommending those in this case). Also take a look at readthedocs.org. If you are documenting a SaaS REST API Swagger has become something of a standard.