As a transport protocol, SCTP is equivalent in a sense to TCP or UDP. Indeed it provides some similar services to TCP, ensuring reliable, in-sequence transport of messages. While TCP is byte-oriented, SCTP deals with framed messages.
A major contribution of SCTP is multi-homing support, where one (or both) endpoints of a connection can consist of more than one IP address, enabling transparent fail-over between hosts or network cards.
SCTP was originally intended for the transport of telephony (SS7) protocols over IP, with the goal of duplicating some of the reliability attributes of the SS7 signaling network in IP. This IETF effort is known as SIGTRAN. In the meantime, other uses have been proposed for the protocol.