New values of the frequencies of SNe are presented and discussed in relation to their use as SF indicators. The rate of core-collapse SNe is correlated to the colors and the FIR excesses of the parent galaxies in the sense that galaxies with blue colors and strong infrared excess have higher occurrence of type II and Ib/c SNe than other galaxies. This is in agreement with the expectation that they contain a higher fraction of massive stars. Instead no correlation is present for SNIa. The SN frequency does not correlate with the galaxy activity probably because searches are unable to discover SNe in the nuclear regions of galaxies.
A number of SNe with spectra similar to those of AGN exist. Their characteristic features are explained with explosion of SNe in dense environments, reminding of cSNR's invoked in the starburst model for AGNs. Some recent, peculiar SNe seem linked to GRB's opening the possibility that at least some GRB's arise from this kind of stellar explosion.