"SEO", "SEO Tools" are the vast subjects. Please let me know about your specific requirement. Which purpose do you want to solve?
You can try this free tool http://www.timwebtool.com/onpage-seo/ If you want to learn how the basic SEO works, then try http://forums.digitalpoint.com/showthread.php?t=2173404
google's adword tool is a great tool. i don't know if that's a tool you had in mind, but check it out for keyword research.
For submissions, I recommend Roboform. If you wanna research links, Backlink Builder (webconfs.com/backlink-builder.php) works like a charm. Those two are my favorite SEO tools.
you must have written the purpose of that tool. Only saying seo tool will not help you. There are a lot for each separate purpose
There's a free version of Traffic Travis (also there's cracked versions around of the paid version) and I use that for all my keyword research/competition research etc.
I like those http://www.webconfs.com http://www.sitemapdoc.com/ Both have lot of free and great tools to use, and some useful articles too !