What could happen when you open-source a hardware project? No, seriously. I hold a fair few radical opinions – one is that ...

Arduino Real Time Alarm Clock DS3231 with TM1638. Arduino Clock with Battery backup (real time clock), Time, Date, Alarm, Temperature, TM1638 seven segment module output and input, Display Sleep mode.

Arduino TM16xx library for LED & KEY and LED Matrix modules based on TM1638, TM1637, TM1640 and similar chips. Simply use print() on 7-segment and use Adafruit GFX on matrix.