STACK (www.stack.ed.ac.uk) is a CAS-based plugin for Ilias and Moodle that allows randomization of mathematical tasks and provides feedback based on individual answers. It is a powerful tool for computer aided assessment and feedback, similarly in formative and summative settings.

International Meeting of the STACK Community 2021 was planned to be held in Tallinn, Estonia and hosted by the TTK University of Applied Sciences (TTK UAS). But due to the COVID 19 outbreak it took place in a virtual environment on April 26-29, 2021 (https://www.stack21.edu.ee/).

This Zenodo Community collects the results of this meeting in the form of papers that have been peer reviewed within the conference community.