I’m trying to dig up the M17 messages on the chipsets, but until then - WiFi is incredibly popular and operates on ISM bands. Same with LoraWan, and I have seen some proprietary 900Mhz mesh devices (I think called Milo(?)).

The M17 project found some low cost transceivers that operate on a pretty low level, and I think those would be relevant for future development on ISM for people wanting to use encryption.