Significance Ferroelectric materials are of great interest for both applied and fundamental reasons. One of the focuses of the community has been to combine ferroelectricity with other properties such as light absorption or ferromagnetism. Unfortunately, these additional properties have been difficult to add to traditional ferroelectrics such as perovskites, and new families of ferroelectric materials are highly sought. Here, we report on a class of ferroelectric materials offering a geometric mechanism of polar instability and a unique set of properties including the extremely rare combination of ferromagnetic and ferroelectric order.