Webgate is an event calendar and filterable bookmarks list in one application.
Create an account to make your bookmark list and add events to calendar. Webgate has also test version of time slots calendar which allows users to book time at another users.
Application core, routing and models fatching data from database are written in PHP. Front end, forms and different calendars are written in vanilla Java Script.
I used XHR to fetch data from backend modules. In several files I changed XHR to JS fetch API.