Effective SEO strategies require much effort and time. Although the market for search engines are highly advanced tools that cost a lot, there are many free SEO tools that can help novice and advanced SEO marketing to save valuable time.
Here is a list of free and tested for their effectiveness SEO online instruments:

1) http://www.alexaranking.com. Displays various domains instead of one. Therefore, it can have immediate results Ranking Alexa traffic instead of writing and search each time separately.

2) http://www.xml-sitemaps.com. Sitemaps are extremely important for websites because they help search engines crawl and index them. This is a free sitemap generator xml.

3) http://www.123promotion.co.uk/directorymanager. You can track your shipments to various web directories and you can also visit regularly to see new directories in the list. You just tick the appropriate boxes display when you filed your website. It is very easy to use.

4) http://www.123promotion.co.uk/ppc/index.php. This is a very powerful tool. Shown, based on the Overture and Wordtracker tools keyword search, similar data, including search figures from the previous month. It also adds the average search engine statistics by hour, day, week, projected figures for the next 12 months and then also a figure for the number of searches can be seen in 3 years from now.

5) http://www.seochat.com/seo-tools/keyword-density. This tool keyword density is useful for helping webmasters / SEO 's achieve their optimum keyword density for a set of key terms and keywords. This tool will analyze your chosen URL and return a table of values ??of keyword density for one, two or three key terms.

6) http://www.mcdar.net/KeywordTool/keyWait.asp. This is another excellent resource. Upon entering the right direction and the keyword will be displayed Pagerank and Back links to pages of the top 10 web sites.

7) http://www.123promotion.co.uk/tools/robotstxtgenerator.php. You can create a robots.txt file free with this resource. Therefore, you will be able to direct the search engines to follow the structure of the pages of your website and also directly to the search engines not to follow and track down your specific web site that does not want to be tracked.

All you have to do is fill in the fields and when you create a robots.txt file to upload to the root of your web server.

http://www.nichebot.com. This website displays data using keywords Wordtracker and Google search results. You just enter the keyword and press the button.

9) http://www.webconfs.com/domain-stats.php. You enter the domain and get: domain age, number of pages indexed, and the number of backlinks. The statistics include Alexa Traffic Rank, Age of the domains, WebRank Yahoo, Dmoz listings, count of backlinks and number of pages indexed in search engines like Google, Yahoo, MSN, etc.

It will help you understand why some of its competitors ranking better than you.

10) http://comparesearchengines.dogpile.com. Shows the first results of three search engines. This tool helps you get all kinds of statistics of your competitor's domains.

11) http://www.marketleap.com/verify/default.htm. This verification tool checks to see if your site is in the first three pages of search engine results for a specific keyword. You enter the URL or keywords and displays by 11 top 30 search engines.

12) http://www.related-pages.com/adWordsKeywords.aspx. This tool generates a list of possible keyword combinations based on lists of keywords that you provide.

You enter a list of terms, one per line or separated by commas. This is very effective for Google Adwords and Overture.

12 Free SEO tools are:
1. Alexa Tools
2. Backlink Tools
3. Code Validation
4. Combined Keyword Suggestion Tools
5. Combo Search Engine Ranking Tools
6. Domain Tools
7. Exchange Link SEO Tools
8. Google Ranking Tools
9. Google Sitemap Tools
10. Keyword Suggestion Tools
11. Related Page Rank Tools
12. Search Engine Position Tools

Gilbert, thank you for your complementary post.

Free SEO Tools are;

1.Whois
2.copyscape
3.Alexa traffic tool
4.Google Keyword suggestion Tool.
5.Backlink watch
6.Keyword Density Tool
7.Validation checker Tool.
8.Favicon Generator Tool.
9.HTML Encryption Tool.

The SEO tools are very useful to do SEO work. It helps to do work fast and easily. You can use Alexa ranking checker, Page Rank checker, Key word Density checker, SERP checker etc. are the best and very important keyword to use.

Seo tools are made to make works easier. The Alexa ranking checker, Page Rank checker, Key word Density checker, SERP checker are covered above. You're free to add link to any free seo tool to do seo work that is not listed above.

Thanks for re-listing the commonly available list of seo tools but main thing to discuss is that all these tool deliver different results.  Why?

All the tools deliver different result because the creators have different objectives in mind while creating them. There are thousands of SEO tools out there some are improvement of the other, some have all in one features while some have basic features, depends on what the webmaster wants to achieve at any given point in time. 
So that is reason you have different result.
That is why is always good to ask around in forum like Cokoye to get people view and have them tell their experience for using a certain tool(s)

I always like google tools. I have seen that using different tools sepcially free ones give different reports. So, better use the one on which you depend for adword or PPC like essential activities.   

People like Google tool for simple reason being that google is popular.
Do you think otherwise?

Quote from: Christian Okoye on 2013-06-26 19:01
People like Google tool for simple reason being that google is popular.
Do you think otherwise?

People run after google and other popular brands because of its popularity and hereby blinding them to see many quality services elsewhere but still some of all the well known companies are cheap,sometimes free with guaranteed customer help.

"....but still some of all the well known companies are cheap, sometimes free with guaranteed customer help"

This is one of important things that take people to some of these brands, not necessary best service, but they have grown to understand what makes costumers to stick to them and they keep on doing that.

Look at google,millions of people are using their API for business and 8 out of 10 people that is a newbie to blogging started with blogger due to its simplicity and easyness.

I use them and also more than that.

Different SEO tools specially free ones give you different picture of a website you are concerned with. It has been my experience. The difference may be because of mapping technology. I use only Google tools to plan for seo or for internet marketing.