http://adeona.cs.washington.edu/ (2008, discontinued)
Adeona is the first Open Source system for tracking the location of your lost or stolen laptop that does not rely on a proprietary, central service. This means that you can install Adeona on your laptop and go — there's no need to rely on a single third party. What's more, Adeona addresses a critical privacy goal different from existing commercial offerings. It is privacy-preserving. This means that no one besides the owner (or an agent of the owner's choosing) can use Adeona to track a laptop. Unlike other systems, users of Adeona can rest assured that no one can abuse the system in order to track where they use their laptop.Adeona is designed to use the Open Source OpenDHT distributed storage service to store location updates sent by a small software client installed on an owner's laptop. The client continually monitors the current location of the laptop, gathering information (such as IP addresses and local network topology) that can be used to identify its current location. The client then uses strong cryptographic mechanisms to not only encrypt the location data, but also ensure that the ciphertexts stored within OpenDHT are anonymous and unlinkable. At the same time, it is easy for an owner to retrieve location information.
Anyone know of a descendant (direct or inspired) of this?
I think only the client is. https://en.wikipedia.org/wiki/Prey_(software) also links to a minimal free software server, presumably independently implemented, not updated since 2013. In any case, it relies on a server. One of the interesting things about Adeona was its use of a distributed hash table.
it would be pretty trivial to get a twister client script running on the laptop to post the location of the laptop, if you can script the finding out of the location. it wouldn't post the location to the DHT, just to a torrent it would then distribute to followers that would find it through the DHT, so it's no worse. you could even make it post it as a DM to yourself, so nobody else would get info about your whereabouts until the laptop is lost, because DMs are encrypted
I did not realize when I asked a year ago, but I guess that one reason there hasn't been follow up is that Google introduced a (presumably proprietary) service in 2013 called Android Device Manager and renamed Find My Device in 2017 that is available on most Android phones in the wild (ie with the Google bits) https://en.wikipedia.org/wiki/Android_(operating_system)#Technical_security_features