TZ-Olson is an Olson time zone database for Squeak. See https://en.wikipedia.org/wiki/Tz_database for background and general information. The class comment for TimeZoneDatabase provides additional details.
The Squeak Chronology package, especially class DateAndTime, represents time in terms of magnitude (seconds relative to a Posix or Smalltalk reference point) and offset from UTC, where the offset allows the DateAndTime to be displayed relative to a local timezone. When combined with Olson time zone tables, any instance of DateAndTime may be displayed for another time zone, and a local time specification in any time zone may be used to create a DateAndTime instance with correct magnitude.
TZ-Olson is a subset of the original TimeZoneDatabase package for Squeak, and replaces it for Squeak images beginning with Squeak 5.3.