Ham radio. 300 baud packet over HF (thousands of miles) is still a thing, as are newer data modes such as PSK31 and the JT family. I'm actively working on 1200 baud projects over VHF FM now. Back in the day BBS was very much in. These days the same tech is more often used for telemetry, tracking etc (APRS). Now you can do it all in software, ref https://github.com/wb2osz/direwolf and friends.
Ham radio doesn't allow for encrypted connections AFAIK, which makes it a lot less interesting to me.
Why wouldn't it allow encryption? Can't anything that sends and receives packets be able to be encrypted?
Not if the law forbids encrypted connections over Ham frequencies :)
Oh I see. A policy restriction and not technical.
The restriction is because commercial activities are prohibited over amateur radio, and encrypted traffic would prevent that rule from being enforced.
I believe there's an exception for controlling remote devices when you need to make sure some rando doesn't brick your pricy gear.