At the first link (below) there are two sections that will be of interest for you:
- the UN system matrix, listing all organizations in the UN system
- Major groups and other stakeholders, containing also a registry of major groups organisations (many NGOs and INGO's are listed there - 3679 entries).
The third link provides a directory of UN System organisations
Permit me to also introduce the Actor Atlas which introduces the notion of social architecture (see 2nd link) and provides a partial thematic classification of organisations in accordance with their area of work ("function of government") (4th link)
Within the same approach one can then add national organisations as is illustrated for the United States (5th link)
There are at least 4.000 international NGOs registered with the UN, but to have a comprehensive list means to do serious research. The network of DRC ONGs (French acronym) listed around 3.600 when I checked last. However, I know one person who - on his own - runs four of them to make a living.
This is a difficult question that I tried to address in a chapter from a slightly different angle - that is, to show that small-scale independent NGOs that have religious affiliations were on the rise. Part of the problem is there is no comprehensive databases that track NGOs / INGOs. And, the livespan of some small NGOs is short, some only a few years. BUT you can estimate from different sources - UN, individual countries do reporting, and the increase application 501c3s in US, etc. The attached article might have some clues as to how I went about arguing for the increase in new small-scale NGOs in the last 10-5 years.
Chapter Do-It-Yourself Missions: The Rise of Independent Faith-Based...