Explore Keywords - Free keyword research tools
SEMRush - All-in-one Marketing Toolkit for digital marketing professionals.
Keyword Spy - Get competitive data on other people's AdWords sem bids.
Lumar - (Previously DeepCrawl) Hosted SEO spider to analyze and find problems with websites.
KeywordTool.io - KeywordTool.io is the best FREE alternative to Google Keyword Planner and Ubersuggest. It uses Google's autocomplete feature to get over 750+ long-tail keywords for any given query.
Website Checker Tech - WebsiteChecker.Tech is SaaS tool that detects SEO and availability issues of your website, making it easier for you to fix them.