Agar-agar is a vegetarian gelatin substitute derived from seaweed. It is sold both in flake and powder varieties, and can be used as a thickening agent for vegan and/or dairy-free recipes. Here are two variations of chocolate pudding: 

Chocolate Coconut Pudding 
3 cups coconut milk 
½ cup cocoa powder 
¼ cup agave nectar and stevia as desired 
2 tablespoons agar-agar 
1 tablespoon vanilla extract 

Mexican Chocolate Pudding 
3 cups almond milk 
½ cup cocoa powder 
¼ cup agave nectar and stevia as desired 
2 tablespoons agar-agar 
1 tablespoon vanilla extract 
1/2 teaspoon chipotle powder 
1/2 teaspoon cinnamon powder 
pinch of nutmeg 

In a sauce pot, combine all the ingredients and bring to a boil, whisking occasionally so there are no lumps. Lower the heat and simmer for at least 10 to 15 minutes to let the agar-agar dissolve completely and thicken properly. Transfer the mixture to a serving bowl or individual ramekins and let cool to room temperature. It will set at room temperature unlike animal based gelatin. Refrigerate and serve cold.