1. A system for sharing a user interface surface that is accessible simultaneously by multiple users through multiple respective sources, the system comprising: a processor; a memory coupled to the processor, the memory comprising: shared surface logic that: generates local canvases responsive to user interactions, including a first local canvas and a second local canvas, wherein the local canvases each comprise local canvas boundaries and a local canvas identifier; generates a first group canvas corresponding to at least two of the local canvases, the at least two of the local canvases establishing a first set of local canvases, wherein the first set of local canvases are respective local representations of the first group canvas and the first group canvas is a shared surface representation of the first set of local canvases; and interaction detection logic that: detects multiple user interactions corresponding to the local canvases, wherein at least one of the detected multiple user interactions corresponds to the first set of local canvases; updates the first group canvas to obtain an updated first group canvas; and updates the first set of local canvases based on the updated first group canvas.