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Recommendations (for and against) are my personal opinion only and may be out of date.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? As of February 2022 I've updated all the sites I look after to Drupal 9 (experience: mixed). I haven't decided how to label future version compatibility as D10 will be coming soon as well. The upgrade_status module is superb. You're bound to have issues with composer. Also watch out for a nasty session headers bug with redirect_after_login.

What about sites still running Drupal 7? In short I still recommend leaving them on Drupal 7. Your decision is really if you will gain anything from Drupal 8/9 and for many then answer will be no, and one of the main hassles - apart from converting each content type one at a time, and setting up a new theme, will be recreating all your views by hand, as views can't be automatically upgraded.

(1 modules in list)
Module name or machine name
Any text in the notes
Name D8 Personally Tested Last Updated
View Migration (view_migration) 2018-11-23

d.o. page

Not recommended

Migrate views from D7 to D8.
Once installed on D7 - you need to go to /admin/config/view-migration 
It outputs multiple YML files and you're specifying a directory to put them in, which you need to create first.

My experience of the YAML output has been:

- incomplete (e.g. multiple missing displays in a complex view, views without a machine name)
- invalid UTF8 due to the next and previous arrows in pager.options.tags being encoded wrong
- the dependencies section at the top of the file not being set out correctly

It doesn't look like there's much current development activity (likewise migrate_views, which is the other plugin people usually mention).