Softcover is a self-publishing platform. I know there are ton of them. What sets them apart is they have open sourced their publishing tool. So you can write your book with markdown or latex and create pdf, mobi, epub files on your own. You are not bound to publish via Softcover. You can host them anywhere.
I have been using their publishing tool for the last month to write a book on hapijs. It is a pleasure to use it as you get the html feedback immediately. I'm able to generate a pdf and share with my subscribers for feedback. I am also using their site to publish the html for feedback. They are also very supportive.
If you are into writing (a new book or converting your blog into book etc), check them out.
I have installed their publishing tool in a docker container. By this way, I don't pollute my machine and also it is useful when I switch machines. You can read about the docker container in this post: Using docker and softcover to write your book.