DS3231 Real Time Clock

• I²c
• Real time clock (date and time)
• Temperature sensor
• 2 alarms
• Programmable Square-Wave Output Signal
• CR2032 backup battery

Datasheet

Libraries

• https://github.com/jarzebski/Arduino-DS3231 : looks feature complete, but unmaintained
• https://github.com/rodan/ds3231 : I don't see temp funcs
• https://github.com/JChristensen/DS3232RTC : looks good, feature complete, maintained, good docs and examples.