The local time zone is obtained from, in order of preference:
1) the user defaults database: NSGlobalDomain "Local Time Zone"
2) the GNUSTEP_TZ environment variable
3) the file "localtime" in System/Library/Libraries/Resources/NSTimeZone
4) the TZ environment variable
5) The system zone settings (typically in /etc/localtime)
6) tzset and tznam on platforms which have it
7) Windows registry, on Win32 systems
8) or the fallback time zone (which is UTC)

If the GNUstep time zone datafiles become too out of date, one can download an updated database from ftp://elsie.nci.nih.gov/pub/ and compile it as specified in the README file in the NSTimeZones directory.

Time zone names in NSDates should be GMT, MET etc. not Europe/Berlin, America/Washington etc.

The problem with this is that various time zones may use the same abbreviation (e.g. Australia/Brisbane and America/New_York both use EST), and some time zones may have different rules for daylight saving time even if the abbreviation and offsets from UTC are the same.

The problems with depending on the OS for providing time zone info are that time zone names may vary wildly between OSes (this could be a big problem when archiving is used between different systems).

Win32: Time zone names read from the registry are different from other GNUstep installations. Be careful when moving data between platforms in this case.