Executive Summary

In mid-December, eight Drupal developers held a code sprint at the Acquia offices in Andover, MA with the goal of “implementing Fields in Drupal core.” The attendees were Dries Buytaert, Yves Chedemois, Florian Loretan, Barry Jaspan, Károly Négyesi, David Rothstein, Karen Stevenson, David Strauss, and Moshe Weitzman.
During the sprint, we hashed out some major architectural breakthroughs, wrote lots of code (including unit tests to make sure the code keeps working!), and organized ourselves to help push through the remaining items which were not able to be completed during the sprint. We achieved our major goal: implement a "Field API" in core that cleanly allows attaching fields to both nodes and users and, by extension, any other entity type that wants them. The rest of the post contains more details about what we accomplished.
There is still plenty to do and we need your help! To jump in, visit our Drupal core improvements: Field API page.
We would like to give a huge thanks to the Drupal community and all of our contributors that made this sprint possible. This experience has proven how important sprints are and how effective they can be, and we hope that each of you will consider donating to see further sprints happen, such as the forthcoming Drupal.org Redesign sprints.