Link shows past work, much has moved to GitHub for Darrell Ulm.
For work that was done further back before GitHub, some information is at: Darrell Ulm, Open Source Software profile at OpenHub, which is an interesting site to show open source contributions.
The link shown on this page includes reference to Darrell Ulm, on 4/2/2008, becomes the 57th code committer to Koha. And here is the History of Koha, and Open Source Integrated Library System.
An early Drupal 8 post, by Darrell Ulm, when Drupal 8 was still evolving is here: Drupal 8 Article: Should you be interested in the new Drupal 8? (by Darrell Raymond Ulm).
And believe this is before the internals of Drupal 8 was re-implemented in Symfony PHP framework as compared to the inherent PHP implementation of prior versions for Drupal and the Drupal 4 5 6 and 7 API.