Farmville and Harvest Moon share a theme and maybe even an aesthetic but are in different genres. Harvest Moon is a single player sim game. Farmville is an async multiplayer invest/express. Zynga popularized the genre.

The closest "rip off" to Harvest Moon would be Stardew Valley, but no one ever refers to it that way because rip off is not a useful term for conveying taxonomy. Rip off is only useful for displaying derision towards genres the writer doesn't enjoy.