The idea behind Rapidez is to have a blazing fast headless frontend for your Magento 2 webshop which should be very easy to customize. The frontend is seperated from the Magento installation and communication between them is done via the Magento REST API and GraphQL. To speed things up Rapidez also queries the Magento database to get catalog information for example. For category pages and the filters Rapidez is using Reactive Search which uses ElasticSearch as database. Indexation is also taken care of and is pretty fast.