This can't be a secret but I have a demo website question...

This can’t be a secret because so many theme authors are doing this…but when I see demo websites, I see menu links that shows off the various blog layout styles for the theme. Pages that use templates are easy enough because they are templates, but how are the different blog layouts able to show from the same blog on the same site on the same demo? Are the blog layouts built into actual page templates with custom queries, bypassing the default method of displaying blog posts in WordPress? Or is this something that is done special just for the demo? Either way, it would be interesting to find out how this is done.

Have a look at WordPress Multisite Network.

Thanks for the reply…however, perhaps there was some confusion in my posting. I am familiar with WP multisite networks, as I use that already. What I was referring to is a “single” demo site style where if you have a blog menu link with a submenu of additional menu items that link to for example, 6 different blog layouts that showcases what that style offers. Such as blog layout 1, blog layout 2, blog layout 3, etc.

You can use PHP GET variables to that

That could just be the page builder or shortcode offering that feature of Choose Layout for your blog. I know Live Composer does that. Themes with options panel for choosing the layout might just have multisite setup with the exact same demo content but demosite/blog-1 might be a totally different multisite than demosite/blog-2

Thanks again for the responses…
@LSVRthemes The Get Variables is a bit out of my comfort zone.

I will see if others will reply as well. With so many doing what I am seeing on demos, there has to be a simple method.

You can also use #hashtags in your URLs and change some CSS classes according to that via JavaScript. But IMHO, get variables are the best solution for this.

BTW, stepping out of your comfort zone is the best way to learn something new;)