"Gengou Lib." is a quick reference of the Japanese era system. This application has functions as below.

- Period picker
- Era picker
- Christian era year picker
- Japanese era year picker
- Show this year button
- Texts can be shown in Japanese or English independently of the default language setting.
- Application badge can show this year number in the Japanese era or the Christian era.

The Japanese era system identifies a year by the combination of the era name (Gengou or Nengou) and the year number within the era. For example, A.D. 2001 is Heisei 13. Please note that two Gengou schemes were used in Parallel from 1331 to 1392 during Nanboku-chō period.

This application would be very useful if you are working with the governments, municipal offices and/or certain companies in Japan.