A divine Scripture, revealed by God, to a Prophet of God to deliver to a people, contains the law of God and the guidance by which the people should follow to earn God's redemption.
The Quran stresses the fact that the Law of God is unchanging (33:62, 35:43, 48:23) and that the only religion decreed by God to mankind is Islam (Submission to God) (see 3:19, 42:13). Essentially, if there is only one religion decreed by God there must be one "Truth". Do we conclude that there should be one Revelation? The answer to this question is that "Truth" and "Revelation" are not absolutely equivalent terms. Since Truth is an absolute term, it is situated independent of form, whereas revelations are relative to time, people and place, and thus require a form. To speak of form is to speak of diversity and thus plurality.
For more info please go to: Introduction to Islam
The Quran speaks of numerous Scriptures revealed across various times. It is the Prophets of God who are given the Scriptures and who are assigned the task of delivering it to their people:
The people used to be one nation, then God sent the Prophets as bearers of news and as warners. He brought the Scriptures down with them bearing the truth to judge among the people in their disputes. 2:213
For more info please go to: Difference between a Prophet and a Messenger
The Quran lists 20 Prophets, with 2 of them (Moses and Aaron) receiving the same Scripture. Therefore, the total number of Scriptures sent to mankind is 19, with the Quran being the 19th and last Scripture.
For more details about this subject please go to: 19th and Final Scripture
The Quran gives the names of a number of Scriptures, they are:
1- Sohof Ibrahim (The pages/books of Abraham) 87:19.
2- Al-Furqaan (the Statute Book/Criterion), given to Moses and Aaron 21:48.
3- Al-Tawrah (The Torah) given to the Prophets of Israel 5:44. The Scripture given to Moses was one of the books which are collectively called the Torah.
3- Al-Zaboor (Psalms) given to David 21:105, 4:163.
4- Al-Injeel (The Gospels) given to Jesus 5:46.
5- The Quran given to Muhammad.
All Scriptures except the Quran have been badly corrupted, with most of them totally lost. However, God promised that the Quran shall be preserved (see 15:9). The preservation of the Quran is guaranteed through an intricate mathematical structure based on the number 19. By means of this structure, the slightest alteration or corruption can be immediately detected.
For more info about the code of 19, please go to: Miracle of the Quran