By adding the URL parameter (i.e. flag) chromeless:true to any Open Publishing Space page you can display that page's content without the global header image, site navigation bar, sidebar and footer - a great way to seamlessly embed Open Publishing Space pages into other systems.
For example, the URL https://demo.hibbittsdesign.org/grav-open-publishing-quark2/ displays the site's home page with the full site around it, but the URL https://demo.hibbittsdesign.org/grav-open-publishing-quark2/chromeless:true will only display that page's content. Any links between Open Publishing Space pages will result in pages being displayed in the same manner.
On Grav 2.1 and newer, the "This page as Markdown (.md)" link below a page's content gets that page as Markdown, ready to reuse – the same as adding .md to the page's address, for example /blog/hero-classes.md, or /index.md for the home page. The link's settings are under Reuse Pages as Markdown in Themes → My Theme, and Grav's Markdown output can be turned off in Configuration → System → Content.
To see a site with more than one guide, publish the example Guides page and Sample Guide (set their 'Published' option to 'Yes' in the Admin Pages panel). The Guides page shows a card for each guide on the site. To use it as the home page, as in Grav Helios Open Reader, set Home Page to /guides in Configuration → System, and turn on Hide from Menu (on the Advanced tab) on each guide's home page to leave the guides out of the menu.
Learn more about the capabilities of the Open Publishing Space project in its README on GitHub.
Want to no longer display this page on your site?
Delete the page 'Read Me' in your Admin Pages panel or set the page's 'Published' option under the 'Options' Tab to 'No'.