There is also https://gitlab.com/tilelessmap/tilelessmap with some of the same focus areas.

> TilelessMap is an open, offline-first mapping engine designed for critical field use, such as forestry, emergency services, and humanitarian work. Built with C and optimized for mobile performance, TilelessMap enables full local map rendering without relying on cloud infrastructure — even in areas with poor or no internet connectivity.

They have an Android app with maps of Yellowstone, Sweden and Norway.

https://play.google.com/store/apps/details?id=org.tileless.m...