I worked with Andreas on the Squeak project several years ago, where I got to see first-hand his outstanding work. Among many other tasks, he played a leading role in actually implementing the Croquet system for eventual consistency. At the time I worked with him, he was developing Tweak, a self-initiated project for rapid GUI development.
On a selfish note, I learned a lot working with Andreas. You only get better in this industry by practicing with good people. Andreas was one of the best.
I'd be remiss not to say he was also a blast to work with. He was always laughing, yet always insightful. He always found ways to get the people around him on a better path. He always found ways to tell them that they were happy to hear.
Rest in peace, Andreas. We are lucky to have had you, for as long as you could stay.