This is a big one as there are many, many SEO tools available - both free and fee based.  So we will start with recommending some on-site SEO tools and we will assume you are not a senior SEO or you probably wouldn’t be reading this post.
Regarding fee based tools, we would recommend either IBP4 [...]

Popularity: 17% [?]

Keyword research is the cornerstone of your SEO plan.  Many website owners dream up an idea for a site, build it, and never truly consider the proper usage of keywords.  It’s critical, as that is how you are found by the search engines and the searchers themselves.
People often start searching with broad results in mind. [...]

Popularity: 19% [?]