Computer-mediated communication is being adopted in work and personal life around the world. Measuring collaborative performance would be useful for evaluating and optimizing social computing applications, but there is a lack of methods for it. For this purpose, we have developed a collaborative block design task, which requires collaboration and depends on simple and abstract rules. The task is about constructing three-dimensional structures out of primitive shapes based on cards representing two-dimensional flat projections of the complete structure. The task is presented as a physical version, which can be manufactured using a 3D printer and a laser cutter, as well as a virtual version which is released as an open source VRChat world created in Unity, and as task components which can be imported into any virtual 3D environment. The task can be used for evaluating systems and augmentations for their fitness for collaboration, as well as to investigate other phenomena which seem to be linked with better cooperation, such as inter-individual and inter-brain synchronization.