John Webster's The Duchess of Malfi and William Shakespeare's Othello both are considered revenge tragedies. This genre, influenced by the Roman playwright Seneca, was extremely common in the English Renaissance, and typically featured evil villains, wronged protagonists seeking vengeance, dramatic plots including betrayals and subterfuges, exotic settings (especially Italy) and bloody violence onstage; corpses litter the stage at the end of most plays in the genre.
The first area of comparison between the plays lies in the nature of the protagonists. The Duchess is an Italian female and Othello a Moorish male. Both protagonists are deeply in love and married to the people they love. In both cases, the relationships are disrupted by external influences. Othello is made jealous by Iago's innuendo about Desdemona. The Duchess is separated from her husband and eventually killed by siblings jealous of her position. While the Duchess and Antonio have children, Othello and Desdemona do not. While both the Duchess and Antonio are killed by antagonists in the play, Othello kills Desdemona and commits suicide.
Perhaps the greatest difference in the play is moral ambiguity. In Webster's play, there are purely good and purely evil characters. The protagonist in Othello is a more complex and conflicted character, capable of great nobility, but flawed and prone to jealousy and rage.