Just to be clear, I'm not looking for mass consumer adoption. I'm looking for the initial signals that prove that somebody is getting sufficient value that it's not just a novelty. E.g., the agricultural uses of drones are not mass market, but they're not just "OMG drone".

The Palm Pilot is an interesting example, but as somebody who had one, they were actually getting used. I used mine daily. When I broke my first, I bought a second. There was also quite a lot of third-party software, including a robust commercial market. E.g.:

https://web.archive.org/web/19991003055719/http://www.zenith...