In Norway we have https://helsenorge.no/smittestopp – The app is up and running since two weeks; research data has been collected about percentage of use and indicates that 50% of the people has downloaded it.
The app SMITTESTOPP also collects anonymized research data. The app is developed by Simula Research lab https://www.simula.no – who answers to questions.
I am impressed that they managed to develop a well-functioning up in such a short time, and my only complain is that it uses some battery. In Norway last week they open the kindergarten and this week the primary school.