Thanks for the replies - interesting and good to know that some types of TCAS can see non-transponder ADS-B
" FLARM doesn't talk to anything other than another FLARM receiver " That's not true - it talks to ground stations, which then rebroadcast the gliders information in a format usable by PilotAware (which is used by many light aircraft).
The Shawbury helicopters also have FLARM