  Remote collaboration systems have become increasingly important in today's
society, especially during times where physical distancing is advised.
Industry, research and individuals face the challenging task of collaborating
and networking over long distances. While video and teleconferencing are
already widespread, collaboration systems in augmented, virtual, and mixed
reality are still a niche technology. We provide an overview of recent
developments of synchronous remote collaboration systems and create a taxonomy
by dividing them into three main components that form such systems:
Environment, Avatars, and Interaction. A thorough overview of existing systems
is given, categorising their main contributions in order to help researchers
working in different fields by providing concise information about specific
topics such as avatars, virtual environment, visualisation styles and
interaction. The focus of this work is clearly on synchronised collaboration
from a distance. A total of 82 unique systems for remote collaboration are
discussed, including more than 100 publications and 25 commercial systems.
