This paper presents DigiTher, a flexible AI-based platform for clinical research on digital therapeutics, enabling personalized treatment plans and real-time monitoring of patient progress. The DigiTher platform has been designed to deliver three specific kinds of Digital Therapeutics, which are mainly based on conducting motivational dialogues with the patients or providing multimedia material to accompany and support patients. Conversational solutions and sensing technology are used to (i) support the management of chronic conditions (e.g., nutritional ones), (ii) run Cognitive Behavioral Therapy (e.g., within mental health management scenarios), and (iii) support Behavioral Enhancement Interventions (e.g., improve lifestyle).