Intelligent agent is a software product which can work autonomously and intelligently on behalf of human workers. It has problem solving methods and knowledge about one particular domain. This paper provides overview of different types of intelligent agents, frameworks used for them and applications of these agents. Five types of intelligent agents are discussed: Mobile agents, Distributed agents, Multiple agents, Collaborative agents and Social agents. Agent frameworks are also explained which are used for the creation of agents, communication between them and discovery of agents. Agent based systems can work all the time. Besides, they have ability to take decisions intelligently. Hence, there are some useful applications of agent based systems in different areas of life in which manufacturing, process control, information management; e-commerce, entertainment, health care and e-education are included.