For Hiring Candidates in Central Government, UPSC and SSC are the major agencies. UPSC Hires candidates for Various Officer Cadre Posts (Mainly Group A and Group B Gazetted) while SSC is responsible for recruiting candidates to the subordinate level posts (such as Inspectors, Assistants, Clerks, DEOs, MTS etc)
For Recruiting Candidates in various Public Sector Banks, IBPS plays the major role which conducts popular exams such as IBPS PO, IBPS Clerk, IBPS SO etc through which it recruits both officer & clerical cadre positions in Public Sector Banks.
Some banks & Financial Institutes conducts their own exam such as SBI, RBI, LIC, ECGC, SEBI, NABARD etc.
Public Sector Undertakings such as GAIL, BHEL, SAIL, NTPC etc and Indian Railway also conducts their own recruitment exams and they have full autonomy in deciding the selection process.
Most of the states also have similar recruitment pattern where State Governments have their own State Public Service Commission / State Staff Selection Commission and State PSUs conduct their own recruitment exams.
Further the Government of India has also announced that it will create a new agency which will be known as the National Recruitment Agency (NRA). It will conduct the preliminary test for SSC, IBPS, Railway etc. However the main examinations will be conducted by the respective agencies. Some of the State Governments have also announced that they will recruit candidates through NRA CET Exam.