There was recently a very good HN thread on Etak [1] including comments from people who've seen it firsthand or have worked on related ventures.
[1] https://news.ycombinator.com/item?id=13744825
Another cassette tape navigation system, this one from 1985, the Etak Navigator:
https://www.fastcompany.com/3047828/who-needs-gps-the-forgot...
https://news.ycombinator.com/item?id=13744825
https://en.wikipedia.org/wiki/Etak
(The Fast Company article is quite good, with interesting photos.)
There was recently a very good HN thread on Etak [1] including comments from people who've seen it firsthand or have worked on related ventures.
[1] https://news.ycombinator.com/item?id=13744825