Modern "acrylic gesso" is a widely used ground that is a combination of calcium carbonate with an acrylic polymer medium latex, a pigment and other chemicals that ensure flexibility, and increase archival life. It is technically not gesso at all and its non-absorbent acrylic polymer base makes it incompatible with media that require traditional gesso such as egg tempera. It is sold premixed for both sizing and priming panels and flexible canvas for painting. While it does contain calcium carbonate (CaCO3) to increase the absorbency of the primer coat, titanium dioxide or "titanium white" is often added as the whitening agent. This allows gesso to remain flexible enough to use on canvas.
The beauty of gesso is that you can apply it to nearly any surface, and then you can paint on that surface with acrylic paint. For example, you can apply a layer or two of gesso to vinyl records, rubber duckies, or cigar boxes, and voila - you can now paint on that object with acrylics! What fun. The possibilities are endless!