Real Time Clock
IC DS1307 is a low power, fully Binary Coded Decimal (BCD) Real Time Clock (RTC) / Calendar with 56 Bytes of General Purpose SRAM. Address and data is transferred though I2C bus. It has built in circuit for detecting power failures and to switch backup battery supply. Current consumption is less than 500nA in battery backup mode. It can be easily interfaced with microcontrollers having I2C modules.
DS3231 RTC and EEPROM Module
This is a module made using DS3231 RTC and AT24C32 EEPROM. DS3231 is an extremely accurate, low cost I2C RTC with integrated temperature compensated crystal oscillator. It also has a built in comparator which monitors the status of VCC to detect power failures and to automatically switch to backup power supply. AT24C32 provides 32,768 bits of serial EEPROM organized as 4096 words of 8 bits each. This gives you 32Kb of non-volatile memory for your projects. This module can be easily interfaced with Arduino Boards, Raspberry Pi and all Microcontrollers.