List of organizations under the United Nations fold under Article 57 of the Charter and act autonomously. They coordinate through ECOSOC (Economic and Social Council).
FAO – Food & Agriculture (Rome)
ICAO – Civil Aviation (Montreal)
IFAD – Rural Development Funding (Rome)
ILO – Labour & Social Protection (Geneva)
IMO – Maritime Affairs (London)
IMF – Monetary Stability & Economic Policy (Washington, D.C.)
ITU – Telecommunications (Geneva)
UNESCO – Education, Science, Culture (Paris)
UNIDO – Industrial Development (Vienna)
UNWTO – Tourism (Madrid)
UPU – Postal Services (Bern)
WBG – World Bank Group (Washington, D.C.)
WHO – Global Health (Geneva)
WIPO – Intellectual Property (Geneva)
WMO – World Meteorological Organization - Weather & Climate (Geneva) Wikipedia
Under the UN Secretary-General’s umbrella, these are more operational:
Departments: DSS, DESA, DGACM, DGC, DMSPC, DOS, DPO, DPPA Wikipedia
Regional Offices:
ESCAP (Bangkok),
ESCWA (Beirut),
ECA (Addis),
ECE (Geneva),
ECLAC (Santiago) Wikipedia
Not quite agencies, not quite departments—but part of the UN ecosystem:
UNAIDS – Leading global response to HIV/AIDS United Nations
UNHCR – Refugee protection & resettlement United Nations
UNIDIR – Disarmament research United Nations
UNITAR – Training & capacity building for UN staff and officials United Nations
UNOPS – Project implementation, infrastructure, procurement United Nations
UNRWA – Refugee aid for Palestinian populations United Nations
UNSSC – Learning for UN system staff (Staff College) United Nations
UNU – UN University: policy-relevant research United Nations
UN Women – Gender equality & women’s empowerment United Nations