Github 
is a web application typically used by developers to store source code files and manage changes made to those files by multiple users.
Historically, one could freely use Github public repositories, which are repositories that anyone with a Github account can access, but had to pay to have private repositories. At the beginning of 2019 Github announced it will start providing free private repositories for up to three collaborators. If you need more than three accounts to be able to access a private repository you will have to pay for that capability.
While Github is primarily used by developers, it has benefits for anyone who needs to synchronize text files across multiple computers. Tools for working with Github are available for just about every operating system platform and you can use those tools to not only sync text files across devices but to also help manage changes to those files so that you don't lose work.
I only have a free Github account so up until this year I have only created public repositories, which is ok because I am not storing anything in those repositories that I don't want anyone else to be able to see.
My primary use of Github has been to transfer text files with my Linux computers without having to install a FTP server. I install Git on my Linux systems if it has not already been installed and then clone my repositories.
I also have Working Copy on my iPad Pro, which I can use to clone repositories from Github to the iPad. I have created my first private repository to store drafts of essays that I am writing. Actually, any text file that I want available across my computers can be stored in that repository.
Working Copy integrates with the iOS Files app, which enables apps that support Files to directly access my repositories in Working Copy. Pretext is one such app and I am using it to edit documents. For more information about this process see this Macstories article .
I launch Pretext, which shows Working Copy in the file picker, tap down in to my drafts repository and tap the name of the file I want to edit. When I close the file my edits are stored in Working Copy.
At this point I do have to open Working Copy to commit and push the edits to the file so that it transfers to Github and can then be pulled down to my other computers.