In the UK an estimated 1 in 4 adults live with long term conditions. The risk of severe fatigue increases with each additional long term condition. This equates to over 500,000 people in the UK living with severe fatigue that negatively affects both mental and physical well-being and limits people's social, physical and work related activities. Better fatigue management would enable people to re-engage with physical activity and social activities, essential for long-term health, well-being and quality of life. The fatigue tracking app helps people with brain injury or long-term conditions track their fatigue across the day, to better understand the factors that trigger or alleviate their fatigue. By balancing their fatigue with their everyday activities the app enhances their mental well-being as they re-engage with physical and social activities. The app provides digital outcomes to evaluate fatigue interventions more effectively and increase efficiency in use of health resources. The app simplifies user data input while the data provides a useful resource for academics researching traumatic brain injury and its treatment/ management. The app can be easily adapted to have an impact on other areas of research and the day-to-day management of lifestyle diseases such as heart disease, type 2 diabetes and obesity. As a research tool, long-term self-monitoring enables researchers to develop fatigue profiles built on intensive individual data but combined at a group level. The app delivers a personalised approach to managing fatigue and forms the basis of developing more effective, personalised interventions. The app uses data from popular wearables such as Fitbit/ Garmin and a points driven rewards system to motivate users to increase their physical activity, provide real-time health data monitoring which allows for adapting exercises and rehabilitation activities based on patient data. Based on patient data, individual goals can be set such as "be active for 20 minutes per day", "walk 2km per day", etc. Goals are displayed on the patient's phone or on a web based platform. The app uses push notifications to nudge users to complete a survey of how they are feeling and what they are doing in real-time whilst passively collecting data about their sleep, and physical activity. Users receive a daily summary of their fatigue and activity. Users can view their daily, weekly and past month physical activity, survey engagement, points collected and rewards in personalised dashboards on the app. Exported data is provided in a number of accessible formats.