Drupal 9 is here , and there are already some useful modules available for the newest stable version of Drupal. Right now for Drupal 9 there is Admin_Toolbar, Redirect, Paragraphs, Metatag, SimpleXML Sitemap, Field Group, Ctools, Entity Browser, Embed, Webform, Entity API, IMCE, Google Analytics, External Links, XML Sitemap, Focal Point, Acquia Connector, and looks like the list just keeps going. For the module search I used "Stable Release" which means it looks like Drupal 9 is really forward compatible from Drupal 8!
Technical notes about past publications and work by Darrell Ulm including Apache Spark, software development work, computer programming, Parallel Computing, Algorithms, Koha, and Drupal. Source code snippets, like in Python for Spark. Retrospective of projects.