191/189/190 and 491 are different visa subclasses for skilled workers who want to migrate to Australia.
Subclass 191: Permanent Residence (Skilled Regional) visa is for skilled workers who want to live and work in regional Australia permanently. To be eligible, applicants must have lived and worked in regional Australia for at least three years.
Subclass 189: Skilled Independent visa is for skilled workers who do not have a sponsorship from an employer, state, or territory government. This visa grants permanent residency to the holder.
Subclass 190: Skilled Nominated visa is for skilled workers who have a nomination from a state or territory government. This visa grants permanent residency to the holder.
Subclass 491: Skilled Work Regional (Provisional) visa is for skilled workers who want to live and work in a designated regional area of Australia for up to five years. To be eligible, applicants must have a nomination from a state or territory government or a relative living in a designated regional area.