Back to first principles, ZoneInfo is incredibly thorough, but that makes it difficult to use for a single gadget. There is a wikipedia list too, but not easily parsed. (If web 3.0 is all about the semantic web, then wikipedia will hopefully become a better home for structured data too.) I then found “City Time Zones” which is a user-generated, wiki-style, approach. The problem is it doesn’t handle daylight savings, but it will do for now – the user will simply get a checkbox to say if it’s daylight savings or not. Yeah it’s a really ordinary solution, but the only one I can manage if I’m to build the gadget in a day or so.

I extracted from the ZoneInfo a simple list you might find useful. The first iteration is sorted by timezone and I’ve junked geo and other info, so you just have the timezone names, the offset, and major locations.

Tonga Standard Time,+13:00 Nuku’alofa
Kamchatka Standard Time,+12:00 Kamchatka
Fiji Standard Time,+12:00 Fiji, Marshall Is.
New Zealand Standard Time,+12:00 Auckland, Wellington
Norfolk Island Standard Time,+11:30 Norfolk Island
Central Pacific Standard Time,+11:00 Solomon Is., New Caledonia
Magadan Standard Time,+11:00 Magadan
Vladivostok Standard Time,+10:00 Vladivostok
Tasmania Standard Time,+10:00 Hobart
West Pacific Standard Time,+10:00 Guam, Port Moresby
AUS Eastern Standard Time,+10:00 Canberra, Melbourne, Sydney
E. Australia Standard Time,+10:00 Brisbane
AUS Central Standard Time,+09:30 Darwin
Cen. Australia Standard Time,+09:30 Adelaide
Yakutsk Standard Time,+09:00 Yakutsk
Korea Standard Time,+09:00 Seoul
Tokyo Standard Time,+09:00 Osaka, Sapporo, Tokyo
Ulaanbaatar Standard Time,+08:00 Ulaanbaatar
Taipei Standard Time,+08:00 Taipei
W. Australia Standard Time,+08:00 Perth
Singapore Standard Time,+08:00 Kuala Lumpur, Singapore
North Asia East Standard Time,+08:00 Irkutsk
China Standard Time,+08:00 Beijing, Chongqing, Hong Kong, Urumqi
North Asia Standard Time,+07:00 Krasnoyarsk
SE Asia Standard Time,+07:00 Bangkok, Hanoi, Jakarta
Myanmar Standard Time,+06:30 Rangoon
Sri Lanka Standard Time,+06:00 Sri Jayawardenepura
Central Asia Standard Time,+06:00 Astana, Dhaka
N. Central Asia Standard Time,+06:00 Almaty, Novosibirsk
Nepal Standard Time,+05:45 Kathmandu
India Standard Time,+05:30 Chennai, Kolkata, Mumbai, New Delhi
West Asia Standard Time,+05:00 Islamabad, Karachi, Tashkent
Ekaterinburg Standard Time,+05:00 Ekaterinburg
Afghanistan Standard Time,+04:30 Kabul
Caucasus Standard Time,+04:00 Yerevan
Tbilisi Standard Time,+04:00 Tbilisi
Baku Standard Time,+04:00 Baku
Arabian Standard Time,+04:00 Abu Dhabi, Muscat
Iran Standard Time,+03:30 Tehran
E. Africa Standard Time,+03:00 Nairobi
Russian Standard Time,+03:00 Moscow, St. Petersburg, Volgograd
Arab Standard Time,+03:00 Kuwait, Riyadh
Arabic Standard Time,+03:00 Baghdad
Turkey Standard Time,+02:00 Turkey
Israel Standard Time,+02:00 Tel Aviv, Jerusalem
Syria Standard Time,+02:00 Syria
Jordan Standard Time,+02:00 Jordan
FLE Standard Time,+02:00 Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius
South Africa Standard Time,+02:00 Harare, Pretoria
Egypt Standard Time,+02:00 Cairo
E. Europe Standard Time,+02:00 Bucharest
Lebanon Standard Time,+02:00 Beirut
GTB Standard Time,+02:00 Athens, Beirut, Istanbul, Minsk
W. Central Africa Standard Time,+01:00 West Central Africa
Central European Standard Time,+01:00 Sarajevo, Skopje, Warsaw, Zagreb
Namibia Standard Time,+01:00 Namibia
Romance Standard Time,+01:00 Brussels, Copenhagen, Madrid, Paris
Central Europe Standard Time,+01:00 Belgrade, Bratislava, Budapest, Ljubljana, Prague
W. Europe Standard Time,+01:00 Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna
GMT Standard Time,+0:00 Dublin, Edinburgh, Lisbon, London
Greenwich Standard Time,+0:00 Casablanca, Monrovia
Azores Standard Time,-01:00 Azores
Cape Verde Standard Time,-01:00 Cape Verde Is.
Mid-Atlantic Standard Time,-02:00 Mid-Atlantic
Argentina Standard Time,-03:00 Argentina
E. South America Standard Time,-03:00 Brasilia
SA Eastern Standard Time,-03:00 Georgetown, South America Eastern Time
Greenland Standard Time,-03:00 Greenland
St Pierre and Miquelon Standard Time,-03:00 St Pierre and Miquelon
Uruguay Standard Time,-03:00 Uruguay
Newfoundland Standard Time,-03:30 Newfoundland
Atlantic Standard Time,-04:00 Atlantic Time (Canada)
Falkland Islands Standard Time,-04:00 Falkland Islands
SA Western Standard Time,-04:00 La Paz
Paraguay Standard Time,-04:00 Paraguay
Pacific SA Standard Time,-04:00 Santiago
Venezuela Standard Time,-04:30 Venezuela
SA Pacific Standard Time,-05:00 Bogota, Lima, Quito
Cuba Standard Time,-05:00 Cuba Standard Time
Eastern Standard Time,-05:00 Eastern Time (US & Canada)
US Eastern Standard Time,-05:00 Indiana (East)
Central America Standard Time,-06:00 Central America
Central Standard Time,-06:00 Central Time (US & Canada)
Mexico Standard Time,-06:00 Guadalajara, Mexico City, Monterrey
Guatemala Standard Time,-06:00 Guatemala
Honduras Standard Time,-06:00 Honduras
Canada Central Standard Time,-06:00 Saskatchewan
US Mountain Standard Time,-07:00 Arizona
Mexico Standard Time 2,-07:00 Chihuahua, La Paz, Mazatlan
Mountain Standard Time,-07:00 Mountain Time (US & Canada)
Pacific Standard Time,-08:00 Pacific Time (US & Canada); Tijuana
Alaskan Standard Time,-09:00 Alaska
Hawaii-Aleutian Standard Time,-10:00 Adak
Hawaiian Standard Time,-10:00 Hawaii
Samoa Standard Time,-11:00 Midway Island, Samoa
Dateline Standard Time,-12:00 International Date Line West

Yes, Tonga is 13 hours of UTC and 25 hours ahead of those little-known places that are UTC-12. In fact, Kiribati Istland (not shown here) is +14 so a day and 2 hours ahead of the others. This wasn’t meant to be easy.

Anyway, I simplified the list further to:

+13:00 Tonga
+12:00 Auckland, Wellington, Fiji, Marshall Is., Kamchatka
+11:30 Norfolk Island
+11:00 Solomon Is., New Caledonia, Magadan
+10:00 Canberra, Melbourne, Sydney, Brisbane, Hobart, Guam, Port Moresby
+09:30 Darwin, Adelaide
+09:00 Seoul, Yakutsk, Osaka, Sapporo, Tokyo
+08:00 Taipei, Ulaanbaatar, Perth, Kuala Lumpur, Singapore, Irkutsk, Beijing, Chongqing, Hong Kong, Urumqi
+07:00 Bangkok, Hanoi, Jakarta, Krasnoyarsk
+06:30 Rangoon
+06:00 Sri Jayawardenepura, Astana, Dhaka, Almaty, Novosibirsk
+05:45 Kathmandu
+05:30 Chennai, Kolkata, Mumbai, New Delhi
+05:00 Islamabad, Karachi, Tashkent, Ekaterinburg
+04:30 Kabul
+04:00 Tbilisi, Yerevan, Baku, Abu Dhabi, Muscat
+03:30 Tehran
+03:00 Moscow, St. Petersburg, Volgograd, Nairobi, Kuwait, Riyadh, Baghdad
+02:00 Turkey, Tel Aviv, Jerusalem, Syria, Jordan, Helsinki, Kyiv, Riga, Sofia, Tallinn, Vilnius, Harare, Cairo, Bucharest, Beirut, Athens, Beirut, Istanbul, Minsk

+01:00 Sarajevo, Skopje, Warsaw, Zagreb, Brussels, Copenhagen, Madrid, Paris, Belgrade, Bratislava, Budapest, Ljubljana, Prague, Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna, West Central Africa, Namibia
+0:00 Dublin, Edinburgh, Lisbon, London, Casablanca, Monrovia
-01:00 Azores, Cape Verde Is.
-02:00 Mid-Atlantic
-03:00 Argentina, Brasilia, Georgetown, South America Eastern Time, Greenland, Uruguay
-03:30 Newfoundland
-04:00 Atlantic Time (Canada), Falkland Islands, La Paz, Paraguay, Santiago
-04:30 Venezuela
-05:00 Eastern Time (US & Canada), Bogota, Lima, Quito, Havana
-06:00 Central Time (US & Canada), Central America, Guadalajara, Mexico City, Monterrey, Guatemala, Honduras, Saskatchewan
-07:00 Mountain Time (US & Canada), Arizona, Chihuahua, La Paz, Mazatlan
-08:00 Pacific Time (US & Canada), Tijuana
-09:00 Alaska
-10:00 Hawaii, Adak
-11:00 Midway Island, Samoa
-12:00 International Date Line West

Also available in cut-and-paste form