A cheap greenhouse bar heater connected to a relay controlled by a Pigrow, i've had this box (bluebox) set up the same for a few years but not in use for the last months - just turned it back on and happy to see it's still working as intended.
Did notice because the OS on the Raspberry Pi is so old that it's using a prior version of python that isn't compatible with a few of the scripts used by the new gui - it should be fairly easy to update it without affecting anything else, though if not i'll copy the config files and install a fresh Raspian (RasberryPi OS) then upload the config files back in place. No rush though it's doing it's job well.