ThomasNet, the website of the Thomas Register of American Manufacturers, is a directory of suppliers, also known as the green books. Its primary purpose is to help buyers find new vendors of products, but it can also be useful for competitive intelligence.
ThomasNet is a leading supplier directory in the US; certainly it has heritage, having started a hundred years ago in print. Within the US, listings are fairly comprehensive - as with most resources, you cannot rely on ThomasNet as your only source of supplier information, but it is worth using as one of the several such tools that a supplier research project will need.
Internationally, ThomasNet has virtually no coverage. It cannot compete internationally with the likes of Alibaba, which given the global nature of supply chains, is a weakness. Slightly making up for that, ThomasNet is one of the organizations behind GlobalTrade.net.
As well as details of products, ThomasNet provides, in certain cases, information about the suppliers, for example the number of employees or certifications achieved.
The information about suppliers and products can be a little sketchy, but ThomasNet is a good starting point in a supplier search in the context of competitive intelligence.