Open hemmed drip edge is used with metal roofing. Usually standing seam roofing. The open hem will help prevent water from wicking (due to capillary action) up, past and behind the drip edge metal.
L Drip Edge
L shape drip edge. Usually used on low slope roof decks. Underlayment is placed on the roof deck and over the fascia, the L drip edge is installed, and the roofing material glued or secured even with the outside edge.