This SASS-ified BS-4 Kit download is a php website that uses server-side includes for common components like header, navigation, and footer. You can reskin the app by merely changing the scss variables. The kit uses Grunt to compile and concatenate js and css files. Feel free to examine the grunt file and make changes as you see fit.
Most elements/components are stock BS4, however I have used a few plugins that perform better than the out-of-the-box Bootstrap. Plugins used: