When Alan Kay’s team at Xerox created the overlapping window user interface, they were working for a document company. Everything was organized around documents mimicking paper, sitting in folders except when being operated on by one application or another.
We don’t need the paper metaphor anymore, but we sure have a lot of 2D paper-oriented legacy stuff laying around. While 3D is pretty clearly winning for new applications in which people work together(*), it hasn’t yet demonstrated something so much better with which to replace all the existing 2D docs and their applications.
The state of user-interface design has provided two ways to deal with this: virtual computer displays embedded into the 3D world, and floating 2D windows. Both are pretty good and have their place.
One avatar is operating an in-world bio-signs display, which is also being shown in the lower left as a 2D panel floating over the view of the virtual room. The text chat is a 2D floating panel in the upper left, while the procedure timer and other applications are in-world.
(*)Without people, there is no realtime collaboration. 2D includes people only as second class abstractions rather than reifing them as first class objects in the communications model. For teaching, training, and working meetings (as opposed to mostly unidirectional sales presentation meeting and lectures), 3D has emerged as the most natural way to show individual presence, and the simplest way to provide enough immersion to give a sense of shared presence.