Useful Drupal modules

Click on the module name for notes, comments, patches.
Recommendations (for and against) are my personal opinion only and may be out of date. Feel free to email with corrections/suggestions.

Why haven't you mentioned Drupal 9? I will be adding this, but as of August 2021, this site you are reading is the only Drupal site of mine I've been able to upgrade to D9, so although you can check D9 compatibility status of all modules (use upgrade_status, it's superb) I can't speak from personal experience about any of them.

(1 modules in list)
Module name or machine name
Any text in the notes
Name D8 Personally Tested Last Updated
Address (address) 2018-11-24

d.o. page

Used to be called addressfield.  Adds one dependency - commerceguys/addressing.

This is a bundle of address fields, the correct combinations are shown depending on which country the user selects via a dropdown.
You can configure which countries are allowed per field instance.
To set the default, use the Manage Form Display tab.

It validates postcodes are in the correct format. 

Also supports 'zones' (groups of countries/subdivisions) for shipping/tax purposes.