These are sites that I know of which let you create non-linear stories, where after each page you give the reader a choice of what to do next (like Choose-Your-Own-Adventure books).
This site allows you to post many different types of stories, including interactive stories. Unfortunately they have recently restricted the ability to create interactives to paying members.
However, there are already a good number of interactives involving diapers and a free membership still allows you to add pages to these.
This appears similar to have similar features to Writing.com but still allows free members to create interactive stories. I'm not aware of any diaper stories posted there yet though.
I don't really know much about this site.
Are there any others?