Ramayana, the story of Rama is known to be existing in 300 different versions. Of all the versions of the stories, Valmiki Ramayana is the most accepted. Apart from Valmiki Ramayana; Adhyatma Ramayana, Ramcharitmanas, Ananda Ramayana and Adbhuta Ramayana are also widely accepted. However, there are also texts which have had less scholarly analysis such as the Agastya Ramayana ascribed to Rishi Agastya. There is very limited analysis on this version. So what are the main differences between Agastya Ramayana and Valmiki Ramayana?
Here's what page 115 of this book says about the Agastya Ramayana:
This Ramayana, written by Sage Agastya contains sixteen thousand Slokas. It is marked by its description of the tale of Bhanupratapa and Arimardana ; and it says that king Kuntala and Sindhumati are born as Dasharatha and Kaushalya. It resembles Tulsidasa's Ramayana. This Ramayana tells that JanakI is found in a place of sacrifice. It also describes various events such as the creation of the ocean ; the cause of the coming up of Rameshvara ; the existence of Rishyamuka Mountain, the origin of Maya and Dundubhi and Kala-vigraha.
And here's what page 45 of this book says:
In Agastya Ramayana (Sanskrit), two sons of a king are unaware that a sage is an enemy or their farher. The sage tells them to hold a ceremony with many holy men, but prepares food made from the flesh of other sages. When a voice from heaven warns the sages of the meal, they angrily curse the two sons to be reborn as Ravana and Kumbhakarna, and their minister as Vibhishana.
And here's what page 414 of this book says:
The Agastya-Ramayana, I am given to understand, makes Mandodari the adopted daughter of Maya, but the real daughter of Mandukt. This must have been suggested as a myth from the word manda in Mandodari.