I'm doing SEO myself as a consultant so it's very important for my business ;-) and I have to disappoint you:

1. SEO is not about "a tool", it relies on a plethora of factors and tasks many of which user solost has already outlined in his comment

2. There is no single tool that will allow you to do SEO work, you need a few tools, I'd say more or less 10 depending on what you actually do. Three weeks ago I compiled a list of the most important ones: http://www.seoptimise.com/blog/2009/07/the-30-free-seo-tools...

Nowadays SEO is more about "killer" content creation, social media and viral marketing than anything else. The basic on site SEO work and link building is trivial and not enough.