These are some of the core features of Joomla 4.
- New improved core UI, based on Bootstrap 4.
- Use of more Joomla Framework packages.
- Refactored event management system.
- Introduction of a service container for global dependency management/injection.
- Removing Mootools from the codebase. JQuery will still be available but not in the core.
- Introduction of framework agnostic web components.
- Faster page loading times.
- New media manager.
- MVC layer improvements.
- Frontend template Aurora.
- Backend template Atum.
(Source: Official Joomla website)