The POSEIDON project aimed to increase the independence and autonomy of people with Down syndrome with the help of technical assistants. It followed a user-centered approach by involving people with Down syndrome and their parents, carers etc. A requirement analysis was the first step of the project. It became clear that people with Down syndrome especially need support in the areas of time management, mobility and money handling. Different applications were developed which were tested and evaluated in two field tests in three countries. Results indicate that POSEIDON can help to overcome daily challenges and that it can increase the autonomy and independence of people with Down syndrome.