Simple full screen clock
– Analog and digital clock can be individually activated or deactivated
– Display the date and days of the week optional
– Displays appointments from the Android calendar or internal events database
– Adjustable background and clock color
– Can be set as a screen saver for Android (“DayDream”) on smartphones and tablets
– Compatible with Android TV devices

This app is open source:
https://github.com/schorschii/FsClock-Android