Stellar core collapses are prodigious sources of neutrinos with a few to a few tens of MeV energy. These neutrinos are messengers of both physics and astrophysics. Thanks to the weakness of their interactions, neutrinos can bring information out from the depths of astronomical objects, from which light cannot escape, to tell us about hidden processes in dense matter. Neutrino-bright objects are also sources of neutrinos which can reveal information about the nature of the neutrinos themselves. This chapter will focus primarily on core-collapse supernovae, the expected neutrino signal and the harvest of physics and astrophysics from them but will mention other potential low-energy neutrino sources as well.