1. IIT-JEE (Indian Institutes of Technology Joint Entrance Examination): This is one of the toughest engineering entrance exams in India, attracting thousands of applicants vying for a limited number of seats in the prestigious Indian Institutes of Technology.

2. UPSC Civil Services Examination (India): Aspirants undergo rigorous testing in this exam to secure positions in the Indian Administrative Service, Indian Police Service, and other high-ranking civil service roles in India.

3. Gaokao (China): The National College Entrance Examination in China is one of the most competitive in the world, with millions of students competing for a limited number of university spots.

4. Bar Exam (Various Countries): The bar exam is a rigorous test for those seeking to become licensed lawyers. Passing rates can be quite low.

5. CFA (Chartered Financial Analyst) Exam: This series of exams is taken by those seeking to become financial analysts. The pass rates are relatively low, making it a challenging qualification to obtain.

6. CCIE (Cisco Certified Internetwork Expert): This is a high-level certification for networking professionals. It requires extensive knowledge and practical skills in the field of computer networking.

7. Medical College Admission Test (MCAT): The MCAT is a demanding exam for aspiring medical students in the United States, assessing their readiness for medical school.

8. Ph.D. Qualifying Exams: Doctoral programs often require students to pass comprehensive qualifying exams, which can be extremely challenging due to the depth of knowledge required.

9. Barrett Scholarship Exam (Oxford University): This scholarship exam is considered one of the most challenging in the world, with only a few students awarded scholarships annually.

10. Chartered Accountant (CA) Exam: This professional certification in accounting is known for its low pass rates and rigorous examinations.

11. LSAT (Law School Admission Test): The LSAT is required for admission to law schools in the United States, and it is renowned for its logical and analytical reasoning sections.

12. USMLE (United States Medical Licensing Examination): This series of exams is necessary for medical licensure in the United States and includes challenging assessments of medical knowledge and skills.

13. French Agrégation: The competitive exam for the French education system selects teachers, and it's considered one of the toughest exams in France.

14. Bar Exam (Japan): The Japanese bar exam is extremely difficult, with low pass rates, and it consists of multiple stages.

15. Chartered Public Accountant (CPA) Exam: This accounting certification exam is known for its rigor and low pass rates, particularly in the United States.

These exams are known for their high level of difficulty, low pass rates, and the intense competition they generate. Success often requires extensive preparation, dedication, and a deep understanding of the subject matter. Many candidates spend years preparing for these exams, and even then, success is not guaranteed.