Cornmeal is made from the same ingredient as cornstarch. The main difference between the two is which parts are used and how they are processed. This directly affects their texture, flavor, and function.
Corn grits differ from cornmeal in that it isn’t as processed (refined). This means that they are usually much coarser than what you get when buying cornmeal (even coarse cornmeal).
Polenta is another ingredient that is pretty much exactly like cornmeal. The two have the same flavor, but their textures differ slightly.
Semolina isn’t a corn-based product. It is made from durum wheat and can also be bought with varying textures. So essentially, it is exactly like cornmeal but made from a different ingredient.
This alternative only really works in baked goods where you can get away with a no-textured product. It also works great as a thickener in soups, sauces, broths, and stews.
Masa harina is a type of corn-based flour made from dried corn kernels soaked in a lime solution. It is a product that can easily be bought in stores or online but is also made at home.