eLoran would be either an excellent alternative, or indeed a prime equivalent of a GNSS. The accuracy achieved was pretty good AFAIK (meters). Applying modern digital receiver technology to a very old-style signal was a good idea.
One really big advantage is that it's very difficult to jam over any appreciable area; you need large antennas to radiate power at those frequencies, not something the ordinary jamming enthusiast is going to fit to their car.... It'll also survive a decent solar storm, unlike a GNSS system.
One disadvantage is that it's essentially a regional system; it'd be tricky to provide a truly global system based on eLoran. So if one's motivation is partly adverturous overseas military operations, it's probably not the thing to go for.
Biting the hand that feeds IT
