Google Search based Keyword tool – this tool is based
completely on the queries in Google Search Engine.
AdWords – this tool deals with the URL of website or the
phrases and descriptive words in it.
Wordtacker Tool – this tool helps the developers greatly
in finding the perfect keywords for the website from the
heap of many.
Good Keywords V3.0 – This is also based on the Google
Keyword research and this free software is available for
windows platform only.
SEMRush – SEMRush deals with the keywords provided by
the Google keywords and the AdWord traffic.
Others – Among some other free keyword research tools
some of the most popular are – SEO Book Keyword
Suggestion, KGen, Wordpot Free keyword Tool, and
NicheBot Classic etc.