IELTS, is designed to test the language ability of the candidates who need to study or work in the country where English is primary language of communication.
TOEFL, Test of English as a Foreign Language is a internet based test (IBT) which is standardized test designed to assess the ability to understand and to use English.
GRE, Graduate Record Examination, is computer based exam. It require for admission in variety of graduate level courses of engineering and management worldwide.
SAT, Scholastic Aptitude Test is a standardized test require for admission in under graduate courses in USA. This test has four tests, with essay being optional.