Related : I'm building https://github.com/laem/cartes, an alternative to Google Maps.
On top of a custom protomaps tileset and a few other MapTiler options (such as satellite and hiking), it packs a search engine, a basic OSM place UI, transit calculators (walk, bike with profiles, transit, car), small features like ruler and favorites, transit maps, photos of places, place search by categories, and the French open source street view Panoramax.
Of course, given the scope, its alpha software.
It's built locally for France and French speaking users, though most of the code is English, some data sets are not. I'm spending ~ 50 % working on transit, lots need to be done.
You can test it here : https://cartes.app.
The aim is not to provide map tiles as an API to other project, but to build a UI on it.