GroupGazer: A Tool to Compute the Gaze per Participant in Groups with Integrated Calibration to Map the Gaze Online to a Screen or Beamer Projection Topics: Analysis Methods and Tools; Collaborative Systems for Teaching, Studying and Learning; Multi-User and Collaborative Systems In Proceedings of the 18th International Joint Conference on Computer Vision, Imaging and Computer Graphics Theory and Applications - Volume 2: VISIGRAPP, 109-116, 2023 , Lisbon, Portugal