Where to find the Utopian Calendar
The Utopian Calendar is referenced in the Wikipedia article for the Darian Calendar.
It’s also referenced numerous times in Tom Gangale’s description of the Darian Calendar.
The Mars Simulation Project uses a variation of the Utopian Calendar, which you can read about here.
The Mars Asset Registry uses an earlier version of the Calendar, with a stretched clock and no short weeks.
The Mars Calendar app by Laurie Harrison features the Kepler Calendar.
More Mars time links
Wikipedia article about Timekeeping on Mars
Tom Gangale’s Martian Time website
Archived version of the Areosynchronous Calendar
The Ares Time Zone System by Dean Little
Papers by Tom Gangale
If you want more detail on the various design choices in the Darian Calendar, this is where to look. No-one has given this subject more attention than Tom Gangale and Marilyn Dudley-Rowley.
Gangale, 2004 - Preference Patterns for Martian Time Architecture
Gangale & Dudley-Rowley, 2005 - Issues and options for a Martian calendar
Gangale, 2006 - The Architecture of Time, Part 2 - The Darian System for Mars