Compare Search Engine Optimization tools & methods
Overture, once a Giant in the PPC insdustry had lost some of its adventage once Google and their PPC, Google Adwords, stormed in.
Back in those days Overture were the PPC management system for both MSN and Yahoo, until purchased by Yahoo and forcing MSN to issue their own version called MSN Ad-Center, which is still considered as the less popular system of the three.
Overture are now basing the data on Yahoo searches and Traffic to determine the keyword popularity.
The keyword selector tool that can be found in Overture PPC or as a standalone at http://inventory.overture.com/d/searchinventory/suggestion/
The keyword selector tool is not the most accurate and does not work completely well with foreign languages, but it is still a good source to get an idea from as for specific search terms popularity. It also suggests more popular similar terms to the keyword you’ve entered.