[Books] 'Books' that aren't on Amazon / Other Retailers

Specifically books that might only be available on places like Royal Road, ScribbleHub, WebNovel, or our own websites.

I have two on-going web serials that I update regularly and like to keep my newsletter up to date on. Ex:

[Serial] has two new episodes out this week! [Character A] encounters something strange in the forest, and [Character B] has a confrontation with the most curmudgeonly of the library’s overseers. Could the two be connected? Read today to find out! [Link To Serial Web Site]

I would love to be able to add the serials as their own books so they show up on the author website and also link to them in newsletter campaigns.

This could also be used for special editions that might only be available via a Book Box or limited collector’s editions that are part of a Kickstarter or other special event.