The Joint Admissions and Matriculations Board (JAMB) is a Nigerian entrance examination board for tertiary-level institutions. The board conducts entrance examinations for prospective undergraduates into Nigerian universities. The board is also charged with the responsibility to administer similar examinations for applicants to Nigerian public and private monotechnics, polytechnics, and colleges of educations. All of these candidates must have obtained the West Africa School Certificate, now West African Examinations Council, WAEC, or its equivalent, National Examination Council (Nigeria), NECO.
Source : wikipedia
They also conduct examinations for some companies at various times.