SEMRush - All-in-one Marketing Toolkit for digital marketing professionals.
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.
Lumar - (Previously DeepCrawl) Hosted SEO spider to analyze and find problems with websites.
Google Trends - Explore Google trending search topics with Google Trends.
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.
Keywords Everywhere - Free browser add-on for keyword volume, CPC & competition