Suppose I want to add some Wordpress plugins (e.g. Easy Appointment) to a few static web sites that do not run on Wordpress. Currently, I want to add just basic plugin features (appointment form and calendar) to my sites. In future, I would like also to add plugins for email notification, payments, etc.
My sites consist of a few HTML and JS files. I will probably need to use some cloud database or CMS but I don't want to move the sites to Wordpress. What is the best way to integrate Wordpress plugins with these static web sites ?