1) Simple, very intense heat without any apparent leavening. Chappattis

2) Chemical raising agents. Soda Bread

3) Commercial yeast.

4) Sourdough

5) A variety of Clostridium bacteria ("Salt Rising Bread")

6) Injection of CO2 under pressure. Dr Dalgleish's Aerated Bread Company

7) Incorporation of layers in the dough. Paratha

Whether this counts as "many" is open to argument.

John