We've been using Adapt for a couple weeks on a new project and have built a couple custom plugins. Here's one we decided to open source:

Detailed Feedback is a drop-in replacement for Tutor that provides more detailed feedback on multiple-choice questions. In addition to the generic correct/incorrect feedback, it also provides answer-specific feedback for each user-selected answer.

Hope someone else finds this useful!

(We'll submit this to the plugin repo once issue #58 is resolved.)