This list came from a page on calendar.mantra.network.
Added a redirect to here and removed the page.
TODO: document the modules on this list, and other date and related modules.
https://www.drupalarchitect.info/articles/time-and-date-modules
Widget
https://www.drupal.org/project/datetime_extras
https://www.drupal.org/project/date_all_day
Augmenter
https://www.drupal.org/project/date_augmenter
https://www.drupal.org/project/addtocal_augment
https://www.drupal.org/project/date_content
Display
https://www.drupal.org/project/daterange_compact
https://www.drupal.org/project/office_hours
https://www.drupal.org/project/oh
https://www.drupal.org/project/optional_end_date
https://www.drupal.org/project/date_time_formats
Add to calendar
https://www.drupal.org/project/addtocal
https://www.drupal.org/project/date_ical
https://www.drupal.org/project/views_ical
https://www.drupal.org/project/event_to_calendar
Fields
https://www.drupal.org/project/duration_field
https://www.drupal.org/project/month_year
https://www.drupal.org/project/month_year_range
https://www.drupal.org/project/year
https://www.drupal.org/project/yearonly
Views
https://www.drupal.org/project/views_daterange_filters
https://www.drupal.org/project/views_dates
Events/Registration
https://www.drupal.org/project/bookable_calendar
https://www.drupal.org/project/bee
https://www.drupal.org/project/bat
https://www.drupal.org/project/event
https://www.drupal.org/project/event_platform
https://www.drupal.org/project/rng
https://www.drupal.org/project/registration