You can publish your notebooks in Markdown or HTML format. Starting at one of your own notebooks, click the More button at the top of the window, then click Publish. From this dialog, click one of the links to open your notebook in a new page, or copy the URL to the clipboard:
The Markdown text is ready to copy & paste into your text editor or GitHub gist. Apart from a stylesheet, the published HTML file is independent of fsnotebook.net, and you can embed it wherever you like. (There’s also a reference to the MathJax scripts at mathjax.org, so that TEX typesetting works.)
Note that your notebook’s sharing list applies to these published links too, so if you haven’t added Read access to ‘Public’ then you’ll need to assign Read access to people individually (and anyone you share it with needs an account at fsnotebook.net). But in any case, before you publish via one of these links, you’ll get chance to make your notebook public if you want to.