Appam (Malayalam: അപ്പം, Tamil: ஆப்பம்) is a type of South Indian pancake made with fermented rice batter and coconut milk. It is a popular food in South Indian states of Kerala and Tamil Nadu. It is also very popular in Sri Lanka where it is commonly referred to by its anglicized name as Hoppers. It is eaten most frequently for breakfast or dinner. It is called Chitau (ଚିତାଉ) Pitha in Oriya, Paddu or Gulle Eriyappa in Kodava. It is known as ආප්ප (Appa) in Sinhala and Arpone (အာပုံမုန့်) in Burmese.
According to Gil Marks "Each of the three separate Indian Jewish communities - Cochin, Mumbai, Calcutta - counts in its culinary repertoire grain dishes called appam."
bowl-shaped thin pancakes made from fermented rice flour. They derive their shape from the small Appachatti in which they are cooked. They are fairly neutral in taste and mostly served with some spicy condiment or curry. These hoppers are made from a batter using rice, yeast, salt and a little sugar. After the mixture has stood for a couple of hours, it can be fried in the appachatti with a little oil. In south-central Kerala, it is mostly served with Kadala (Chickpea) curry mutton or vegetable stew or egg roast.
Another form of Appam, where "Kallu" (Malayalam/Tamil) means toddy is added to the fresh batter to kick start the fermentation.
the same as plain hoppers, but an egg is broken into the pancake as it cooks
Milk hoppers (Palappam)
have a spoonful of thick coconut milk/coconut cream added to the doughy centre. When cooked, the centre is firm to the touch but remains soft inside and is sweeter as a result of the coconut milk.
crispy pancakes cooked with a generous amount of palm treacle. Some people also like to add some jaggery just before serving to make it extra sweet.
String hopper (Noolputtu)
Or idiyappam (pronounced [iʈijapːam]), is made from ricenoodles curled into flat spirals. It is served for breakfast with a thin fish or chickencurry, containing only one or two pieces of meat, a dhal (lentil) dish, and a spicysambol or fresh chutney. String hoppers are made from steamed rice flour made into a dough with water and a little salt, and forced through a mould similar to those used for pasta to make the strings. They are cooked by steaming. These hoppers can be bought ready-made. The Indian and Sri Lankan population eats String Hoppers for breakfast or dinner. There are many variations to this, depending on the type of flour used etc. This simple dish can be adapted into other foods such as String Hopper Biriyani, by adding scrambled eggs or vegetables. Another example is located in Kerala, 'Idiyappam' Paaya(Goat Leg Soup made using Coconut).
(also called INRI appam or indri appam) is made by Nasrani Christians in Kerala during Pesaha (Passover). This type of appam is dipped in syrup or Pesaha Pal (Passover Coconut Milk) before being served.
A deep fried rose cookie made with rice. A signature Syrian Christian food as per K.T.Achaya 
which owes its origins to Kerala. This is made with rice flour, jaggery, clarified butter ghee. Unni appam is a variation in which mashed plantain is added to the batter. The batter made out of rice flour, jaggery and plantain is poured into a vessel called Appakarai or Appakaram, which has ghee heated to a high temperature. The appams take the shape of small cups, and are fried until deep brown. Both neyyappam and unni appam are eaten as snacks. This is festive sweet, made on Gokulashtami - the birthday of Hindu deity, Krishna. It is also a common prasadam in Kerala temples.Also a signature Syrian Christian food as per K.T.Achaya 
is made from rice flour, sugar, and coconut. The dish is made by steam-cooking the batter, and is very similar to the Bánh bò from Vietnam.
The presence of Tamils in Malaysia has over the years led to the popularity of the appam. Appam is the term used for a steamed cup-cake sized dessert made from rice flour that is eatened with shredded fresh coconut. The string hopper (local name: putu mayam) is also popular among Malaysians. Sold by street vendors on modified motorbikes, the string hoppers are eaten with grated palm sugar (gula Melaka) and shredded fresh coconut. Malaysian Indians tend to make their own and eat it with either curry or dhal dish.