Eight bikes, a junction, amber light. Four get through, four don't. Five minutes later the group is strung out over ten kilometres. The front doesn't know whether to slow down, the back doesn't know whether the front turned off somewhere. It ends the same way every time: someone at a petrol station with their helmet on the tank, phoning round, while the others circle the area.
An intercom doesn't solve it. A Cardo or Sena reaches a few hundred metres, maybe a kilometre, and the link drops at precisely the moment the convoy splits. Group chat doesn't either, nobody types while riding. And "we're behind you" doesn't say whether that's one bend or three villages.
Sextant is a page you open on your phone. One of the group creates a group, drops the link in the chat, the others tap it and type a name. That's it, nothing installed, no account. From then on everyone sees in their bar mount the distance in metres and an arrow to every other rider. Pete 1.4 km, Mike 300 m. The numbers move while you ride, so you see someone dropping back before they vanish, and the arrow tells you whether they're behind you on the route or went a different way.
It works better on a motorcycle than anywhere else, for a simple reason: the phone is already in a mount and usually on a charger. The main objection to a browser-based tool, that the screen has to stay on and it eats battery, just doesn't apply.
Free, no account, iPhone and Android. Works the same for everyone in the group.
It needs signal. Without it, positions stop updating, so in the mountains or deep in a forest it's not a replacement for a satellite communicator. And the screen has to stay on, which the app asks for itself. On a bike both of those are fine; I'm not pretending otherwise.
When you stop for lunch and are looking for each other in the car park, under a hundred metres it switches to a radar view. Whoever stayed home can follow the trip from a laptop in watch-only mode without sharing anything. And which road each rider actually took when the group split shows up as a trail on the map.
Only the people with the link. The group key sits in the address after the # sign, and that part of an address is something a browser never sends to a server. So the server only relays encrypted data it has no key for. Nothing is stored, IP addresses aren't logged, the group expires by itself after the trip. Treat the link like the key to your garage.
Same problem on a bicycle: who fell behind on the group ride.
And more generally on sharing location without installing anything, and how it differs from Find My or Life360.