This is correct. It's not open source as the HN crowd would know it. OSINT as you say is the correct "Open Source" moniker. Source: I use Maltego for work daily.
>[...]the term "open" refers to overt, publicly available sources (as opposed to covert or clandestine sources). It is not related to open-source software or collective intelligence.
There are bits and pieces, but not a complete tool that gathers all the same functionality (that I'm aware of, there could alays be something new that's not well known yet).
The main selling point of Maltego is the large amount of plugins and data sources that you can integrate with it.
It is of continuous disappointment to me that there really isn't not only a good FOSS link-analysis tool, but doesn't appear to be any of any quality. I've used yED in a pinch a couple of times but it's not FOSS.
This, and the fact that a lot of organisations use data-sources which are so exclusive and expensive that they dwarf Maltego, so nobody is concerned with the cost of a Maltego license.
Other shops will have their own bespoke versions of a Maltego-like tool, but yeah, nothing in the Open Source. MISP probably comes closes to having some of the features.
