Building Bridges and Bonds (B3), a federally funded study of Responsible Fatherhood programs, is testing a set of innovative approaches designed to help fathers advance their parenting and employment skills. One of these innovations is a new smartphone-based application called DadTime. It is one of the first mobile applications specifically designed to help fathers improve their engagement with and attendance at parenting programs. This brief, the second in a series of publications on B3, describes how MDRC collaborated with fathers to develop DadTime. The first brief, "Three Innovative Approaches to Serving Low-Income Fathers," which was published in April 2017, introduced the B3 study and described three new practices for Responsible Fatherhood programs, including the creation of DadTime, which is described in greater detail here.