Principal Findings
We have presented the design of an unguided cCBT–based multicomponent intervention, TreadWill, aimed at high user engagement and universal accessibility. A fully remote RCT with 598 participants was performed to test the effectiveness of TreadWill in reducing depression- and anxiety-related symptoms. The results of the trial show that the full-featured (experimental) and the plain-text (active control) versions of TreadWill effectively reduced both PHQ-9 and GAD-7 scores for the participants who completed at least 3 modules compared with the waitlist control group. The number of participants who completed at least 3 modules in the experimental group was nearly 3 times more than in the active control group. The extra features included in the experimental version increased adherence compared with the active control version in terms of both the time of engagement and the number of modules completed. The results also showed that the number of modules completed correlated with the reduction in the symptom severity of a participant.Two automated surveys presented during the intervention for taking participant feedback showed that the participants perceived TreadWill as useful and easy to use and found most of the interactive features helpful. In addition, the feedback provided by the participants using 