3
Have a look at Duplicati, it's free and open source (LGPL), Source Code on Github. It supports a lot of backup endpoints including of course local external hard drives.
It has a user interface, works on Windows 10 and supports encryption.
2
Check out this link.
https://wiki.openstreetmap.org/wiki/Android
Heaps of options, and it does mention open source options. All will use OpenStreetMaps as the map and routing.
The Maps.Me solution looks pretty good - https://wiki.openstreetmap.org/wiki/MAPS.ME
Navit seems to be more focused on in-car navigation, which might be more suitable depending upon ...
1
Nebula Graph is an open source graph database written in C++. It also supports index. Take a look and see if it fits your needs.
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