A Smoking Cessation App for Nondaily Smokers (Version 2 of the Smiling Instead of Smoking App): Acceptability and Feasibility Study - Bettina B Hoeppner; Kaitlyn R Siegel; Hannah A Carlon; Christopher W Kahler; Elyse R Park; Susanne S Hoeppner (JMIR Formative Research, 2021)