"Writeabout" is a web-based application specialized in writing that enables the implementation of synchronous and asynchronous formative writing tasks and the provision of written and oral feedback. Nonetheless, empirical research on the effects of this software on students' learning outcomes is extremely scarce. Thus, this study designed an English course incorporating formative online writing tasks and feedback mediated by "Writeabout" for 933 non-English major students (77.6% female, 22.4% male) at one autonomous university in southern Thailand. The pre- and posttest writing scores of students were compared, and a significant difference was noticed (t (932) = 38.49, p <0.001). Formative online writing activities were found to predict students' accomplishments on the posttest writing (F (932) = 11.03, p <0.001). Female and male students would receive similar learning outcomes in this case, but their proficiency levels would result in variances. The current study advances our understanding of how incorporating an online application may benefit EFL students.