1. Anchor Text Over Optimization Tool

http://www.removeem.com/ratios.php

Category: Technical SEO

Ensure your site is not over-optimized with its anchor text? Simply type in your URL for a full report of which links might raise flags.

2. Bing Webmaster Tools

http://www.bing.com/toolbox/webmaster

Category: Diagnostic

Similar to Google Webmaster Tools, Bing offers a suite of interesting research tools and resources for webmasters.

3. Bitly

https://bitly.com/

Category: Social, Analytics

Most people use Bitly for URL shortening, but the real power of this platform comes from its analytics.

4. Boomerang

http://www.boomeranggmail.com/

Category: Email, Productivity

Boomerang lets you follow up on emails, even when you forget. Great for link building or any time you send a lot of emails.

5. Buffer

https://bufferapp.com/

Category: Social

Optimize your online social media sharing. Buffer allows you to share with your audience at the optimal times for greater visibility.

6. BuiltWith

http://builtwith.com/

Category: Competitive Intelligence

Use BuiltWith to discover what technology nearly any website was, well, built with. Great for competitive intelligence as well.

7. Buzzstream Tools Suite

http://tools.buzzstream.com/link-building

Category: Link Building, Tools Suite, Email

Most people know Buzzstream as an outreach platform, but they also offer a number of free link-building tools. This company gets it.

8. Caption Tube

http://captiontube.appspot.com/

Category: Video

Free and easy resource used to create captions for YouTube. Helps with usability and offers viewers a readable transcript.

9. CircleCount

http://www.circlecount.com/

Category: Social, Analytics

Google+ analytics ramped up. Free resource to track your followers and analyze your shares. See how many followers you’ve gained over time.

10. Content Strategy Generator Tool

http://seogadget.com/content-strategy-generator-tool-v2-update/

Category: Content

This tool from SEOgadget helps you plan your content strategy intelligently, using keyword research and estimating your audience size.

11. Convert Word Documents to Clean HTML

http://word2cleanhtml.com/

Category: Content, Productivity

Despite the rise of Google Docs, Word still dominates much of the world. Copying and pasting has always been a hurdle, but this tool makes it easy.

12. Copyscape

http://www.copyscape.com/

Category: Content

Copyscape serves both as a plagiarism checker and a duplicate-content checker. Great to use if your content has been distributed across the web.

13. Domain Hunter Plus

http://domainhunterplus.com/

Category: Link Building

This magic extension for Chrome not only helps you find important broken links, but also tells you if the links point to an available domain.

14. Easel.ly

http://www.easel.ly/

Category: Infographics

Free tools for creating and sharing inforgraphics. The templates allow anyone to create a professional-looking graphic.

15. Email Format

http://email-format.com/

Category: Email, Productivity

Email Format helps you find the proper structure for thousands of companies and organizations across the web.

16. FindPeopleonPlus

http://www.findpeopleonplus.com/

Category: Social

The ultimate Google+ directory that’s great for research, outreach, and link building. Sort by keywords, profession, country, and more.

17. Frobee Robots.txt Checker

http://www.frobee.com/robots-txt-check

Category: Robots.txt, Technical SEO

Many robots.txt files contain hidden errors not easily visible to humans. Run your file through this tool and you never know what you’ll discover.

18. GetListed

https://getlisted.org/

Category: Local, Moz

This awesome local SEO tool scores your local SEO visibility and gives you actionable next steps to raise your score.

19. Google Keyword Planner

http://adwords.google.com/keywordplanner

Category: Keyword Research

The tool to replace Google’s popular keyword tool has been derided by some, but still offers data not available anywhere else.

20. Google Analytics

http://www.google.com/analytics/

Category: Analytics

The most popular of all the analytics tools available, Google Analytics continually innovates and sets the standard.

21. Google PageSpeed Insights

https://developers.google.com/speed/pagespeed/insights

Category: Speed

Tools, data, and insights to improve your page speed. Page speed is correlated with better rankings and user engagement, so this matters.

22. Google Trends

http://www.google.com/trends/

Category: Keyword Research

See what’s trending in Google search results and view keyword search popularity over time. A must for trends.

23. Google Webmaster

http://www.google.com/webmasters/

Category: Tools Suite, Diagnostic

The interface recently received an overhaul, and Google Webmaster remains a must-have resource of diagnostic and health tools for site owners.

24. IFTTT

https://ifttt.com/

Category: Productivity

IFTTT stands for IF This, Then That. The tool allows you to create automatic triggers between various apps, like Gmail and Twitter.

25. Infogr.am

http://infogr.am/

Category: Infographics

A great free Infographics resource that allows you to easily create graphics and data visualizations.

26. Internet Marketing Ninjas SEO Tools

http://www.internetmarketingninjas.com/tools/

Category: Tools Suite

The Ninjas are some of the best SEOs and online marketers out there, and they’ve put some of their best tools online for free.

27. Linkstant

http://www.linkstant.com/

Category: Link Building

This nifty analytics tool alerts you anytime someone links to your website. Great for outreach and intelligence gathering.

28. MailTester.com

http://mailtester.com/

Category: Email

Need to send an email to an untested address, but you don’t want to spam them? Check it first with this mail tester to verify.

29. MyBlogGuest

http://myblogguest.com/

Category: Link Building, Content

Guest blogging is still alive and thriving. MyBlogGuest helps you find the good opportunities out there.

30. Panguin Tool

http://www.barracuda-digital.co.uk/panguin-tool/

Category: Analytics

This awesome tool connects with your Google Analytics account to help you see if and when you’ve been hit by Google Algorithm updates.

31. Pingdom

http://tools.pingdom.com/fpt/

Category: Speed

Pingdom offers an entire suite of speed tools to help analyze page load, DNS issues, and connectivity.

32. Piwik

http://piwik.org/

Category: Analytics

Piwik is a lightweight web analytics solution, and a great alternative to Google Analytics.

33. Rank Checker for Firefox

http://tools.seobook.com/firefox/rank-checker/

Category: Rank Tracking

This light and easy desktop tool checks rankings with the click of a button. Quick, easy and free.

34. Rapportive

http://rapportive.com/

Category: Email, Link Building, Productivity

Rapportive works with your Gmail inbox to give you near-instant rich contact information for almost everyone you want to reach. A must-have for marketers.

35. Schema Creator

http://schema-creator.org/

Category: Structured Data, Technical SEO

Everyone loves using Schema.org, but the microformats are difficult to write by hand. This generator from the folks at Raven simplifies the task.

36. Scraper for Chrome

https://chrome.google.com/webstore/detail/scraper/

Category: Productivity

If you’ve never scraped a webpage, you’re missing out. Scraper for Chrome puts the power of simple web scraping in your hands without the need for code.

37. Seer Toolbox

http://www.seerinteractive.com/seo-toolbox/

Category: Tools Suite, Analytics, Link Research

SEER opened up its internal toolbox for everyone in the world to use. These are the same tools used in-house at SEER, and they rock.

38. SEO Toolbar

http://tools.seobook.com/seo-toolbar/

Category: Tools Suite, Toolbar, Technical SEO

On of the most popular tools available, The SEO Toolbar puts a ton of information at your fingertips including backlinks and competitive research.

39. SEO Tools for Excel

http://nielsbosma.se/projects/seotools/

Category: Tools Suite, Analytics, Social

You don’t need to be an Excel ninja to use Niels Bosma’s SEO Tools for Excel. This plugin does so many things many SEOs won’t work without it.

40. Ubersuggest

http://ubersuggest.org/

Category: Keyword Research

Every SEO loves Ubersuggest for its ease of use and wealth of keyword research ideas. Utilizing the power of Google Suggest, it returns hundreds of potential results.