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Recommendations (for and against) are my personal opinion only and may be out of date.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
Views Aggregator Plus (views_aggregator) 2021-05-12

d.o. page

Provides extra options for aggregating data in tables - e.g. grouping sets of rows together and summing the values of particular fields.

Has a hook - hook_views_aggregation_functions_info() - which lets you add your own options to the table aggregation settings - e.g.  supposing you have a limit for something (number of tickets, nights of accommodation) and want to decrement it - you can write a method to sum the matching rows and then do a calculation on the total.

Also supports 'add column function' - adds a grand total (or other summary field) at the very bottom of the table.

Caution - this module breaks hook_views_pre_render() - you can write your own pre_render method to remove or shuffle entire rows, but any chances to values will be overwritten (discovered this by looking through the source and looking for the use of that hook).  The workaround is to try and do what you need to by using hook_views_aggregation_functions_info() instead.