Enables guanyl-nucleotide exchange factor activity. Involved in several processes, including asymmetric protein localization involved in cell fate determination; mitotic cytokinesis; and regulation of actin filament-based process. Located in cell cortex. Expressed in several structures, including P1.p; germ line; hermaphrodite gonad; neuroblasts; and somatic gonad precursor. Is an ortholog of human ECT2 (epithelial cell transforming 2).