If you are technically inclined, there's QGIS. It's a steep learning curve but it is capable of doing ANYTHING as far as maps are concerned. Okay, maybe not anything, I admit it's above my skill level to use effectively. You can import data sets with it, effectively it's more of a map aggregation and editing tool. It's far more capable than OSM and you can work offline once the data sets are imported.

There's also Marble, not the same thing as the other suggestion I see commented. It's got a version for QT and GTK and some appimages out there. It's not as polished. In fact, it's kind of like MS Encarta Atlas, just not really modern. It has a bit of the 'old internet' feel to it, if that makes sense.