A software defined radio server. Lives up top of an antenna mast running off PoE with an RTL tuner connected.
ADSB receiver, similar to above, but on a fixed frequency.
The above 2 could be virtualised in theory, but there is an advantage in having the cable to the antenna short and thus the sbcs live up antenna masts in an enclosure.
MMDVM hotspot for ham radio (this might not count as it HAS TO use the gpio pins on the pi, this can’t be visualised even with a USB port passed through.
As an audio server that would bitstream 24bit/96kHz to an amp.