Disavow Tool

Most site owners don't need to use the Disavow Tool, so Google makes it hard to find. But if you do, it can help you get penalties removed, and some SEO experts swear by it as a way to fight off negative SEO. If you decide to use this tool, be careful and read this guide to disavowing the right links.

URL Opener

The fact that this SEO tool is free to use is an additional advantage. You may open many URLs using URL Opener with only one click.

Link Explorer

Link Explorer has 35 trillion links, which makes it the largest and most accurate link index and the most accurate DA and backlink checker in the SEO world today. The free account gives you access to 10 queries and 50 rows of data per query every month. It also adds basic link metrics to the MozBar as you browse the web.

Link Miner

Link Miner is a free add-on for Chrome that was made by Jon Cooper, who is one of the best at building links. Use it to quickly find broken links on each page and see basic link metrics as you search Google. Easy, simple, and useful.

Detailed

Detailed is a free link research engine that is unlike any other. It was made by marketing genius Glen Allsopp (you can find him in the comments below). Detailed focuses on what's getting people to link to some of the most popular niches on the web, leaving out the extra fluff that can slow down the process of reverse engineering. Oh, and he has a great newsletter.

Backlink Checker

A lot of people don't know that Ahrefs has a pretty good free backlink checker, but they do. It is not as good as their full-fledged paid tool in a number of ways. You can only check up to 100 links, and you can't search by prefix or folder. However, it's useful for quick link checks and SEO on a budget.

Google My Business

This is basically the most important tool for Local SEO, especially if you live in a market that Google serves. It lets you do things like claim your business, change information about your listing, and respond to reviews. Claim your business profile. This is an important step because it's the basis for most other local SEO activities.

Google Review Link Generator

The Google Review Link Generator by Whitespark solves a simple problem: how do you give your customers a URL so they can leave a Google review for your business? Reviews are a big part of rankings, but Google doesn't make it easy to get reviews. This tool makes it simple.

Local Search Results Checker

One of the hardest things about Local SEO is figuring out rankings from any location. This is especially true when Google insists on showing you results from where you are. BrightLocal solves this problem with a quick local ranking tool that lets you check real local rankings from almost anywhere on Earth.

Moz Local Online Presence Tool

How consistent is the information about your business and its location on the web? Moz Local makes it easy to see how your business is listed in the major data aggregators that Google and other search engines use to rank local search results. Very helpful to know what you're good at and what you need to work on.

Mobile First Index Checker

Websites' mobile versions are often very different from their desktop versions. Google has switched to mobile-first indexing, so it's important that the main parts of both versions (links, structured data, etc.) are the same. Several tools can help you check this, but Zeo's is probably the most thorough.