writes "Synchronized with the northern winter solstice and the UNIX Epoch, the terran computational calendar contains 13 identical months of 28 days each in addition to a short Month Zero containing only new year's day and a single leap year day every four years (with the exception of every 128 years). The beginning of this zero-based numbering calendar, denoted as 0.0.0.0.0.0 TC, is on the solstice, exactly 10 days before the UNIX Epoch (effectively, December 22nd, 1969 00:00:00 UTC in the Gregorian Calendar). It's "terran" inception and unit durations reflect the human biological clock and align with astronomical cycles and epochs. Its "computational" notation, start date, and algorithm are tailored towards the mathematicians & scientists tasked with calendrical programming and precise time calculation.
There's a lot more information at terrancalendar.com including a date conversion form and a handfull of code-snipits & apps for implementing the terran computational calendar."