Mobile WACh is an open-source SMS messaging platform designed to enhance communication between clients and healthcare workers (HCWs). It automatically sends scheduled pre-composed messages and allows clients to reach out to HCWs for personalized assistance. The platform features a dashboard for HCW task management, patient tracking, and message translation, as well as the ability to collect SMS metadata and track significant events like childbirth. Mobile WACh has been utilized in eight studies, including four randomized controlled trials, with a focus on improving reproductive, maternal, neonatal, and child health outcomes. The intervention messages are customized based on formative research and behavioral theory to effectively address specific health targets, which include sexual and reproductive health, maternal and child health, communicable diseases, and mental health.