Agar Agar is a seaweed based gelatin. It is a great vegan substitute for grocery store gelatin and can be used in the same way to make puddings, marshmallows, and jellies or as a general thickener. Make sure to dissolve in warm water before adding to your dish. Raindrop cakes are Japanese inspired cakes made of water and agar agar and topped with soybean powder and black sugar syrup.