The French Republican Calendar or French Revolutionary Calendar is a calendar
proposed during the French Revolution, and used by the French government for about
thirteen years from late 1793 to 1805, and for 18 days in 1871.

The first day of each year was that of the autumnal equinox. There were twelve months, each
divided into three ten-day weeks called décades. The tenth day, décadi, replaced Sunday as
the day of rest and festivity. The five or six extra days needed to approximate the solar or
tropical year were placed after the months at the end of each year.
Each day was divided into ten hours, each hour into 100 decimal minutes and each decimal
minute had 100 decimal seconds. Thus an hour was more than twice as long as a conventional
hour; a minute was slightly longer than a conventional minute; and a second was slightly
shorter than a conventional second. Clocks were manufactured to display this decimal time,
but it did not catch on and mandatory use was officially suspended April 7, 1795, although
some cities continued to use decimal time as late as 1801.

More about that here:
http://en.wikipedia.org/wiki/French_Republican_Calendar

Vive la France!

Best regards,

Luciano