If you want to apply to an MBA program at a business school, you'll probably need to take the GMAT(Graduate Management Admission Test). It tests your ability to analyze, write, use numbers, talk, and read.
IELTS evaluates your English language proficiency and is widely accepted by colleges in the UK, Australia, Canada, and other English-speaking nations. It is similar to the TOEFL.
Similar to the SAT, the ACT(American College Testing) is also used for undergraduate admissions in the United States and measures skills in English, math, reading, and science.
If you want to study in Japan but don't speak Japanese very well, you might have to take the JLPT to show how well you know the language.