Some substitutes for gelatin are agar and carrageenan. These seaweed-derived products are vegan-friendly and can be used to replace gelatin in many different recipes.
Agar is available in bar form, powder and flakes, and it provides a firm set. Bar or flake forms should be finely ground in a food processor for best results. It can replace gelatin in equal amounts, and it must be cooked in liquid until it dissolves. One teaspoon of agar powder or 1 tablespoon of flakes can set 1 cup of liquid, and it does not require refrigeration to set.
Carrageenan can be used to set softer foods such as puddings. It must be rinsed thoroughly and soaked in water until it swells. Once soaked, it can be added to liquids, 1 ounce of carrageenan per cup, and boiled for 10 minutes. Strain out the carrageenan after boiling.