Antenati, the Italian Ministry of Culture's portal, is free, requires no account, and holds well over one hundred million images drawn from the State Archives. It is organised geographically, not by name: choose the State Archive for the province, then the comune, then the record type and year, then use the index bound into each volume to find the act number. A name search exists, but only a fraction of the collection has been indexed by volunteers. Try it first; expect to browse.
FamilySearch is free with an account and offers indexed collections alongside images, though some images can only be viewed at a Family History Center or affiliate library. It also holds digitised Jewish community records for certain cities, including the community registers of Mantua.
Neither collection is complete. A record's absence online is not evidence of its absence.