What are 3 categories of financial institutions?

The 3 categories of financial institutions are Central Banks, retail and commercial banks, and investment banks.You can read about the Development Finance Institutions (DFI) – Objectives, Sector Specific DFI in the given link.

Further readings:

1. Types of Non Banking Financial Institutions India
2. World Bank Group – IBRD, IDA and 3 other institutions (UPSC Notes)