We switched to Nightwatch from Stat after some issues and realizing they support wide range of functionalities with have a more friendly interface. Happy so far!
Moz - Backed by industry-leading data and the largest community of SEOs on the planet, Moz builds tools that make inbound marketing easy.
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.
Serpstat - Search analytics, Rank tracking, Backlink analysis and Site Audit tool.
Google Trends - Explore Google trending search topics with Google Trends.
SEO Tools Centre - SEO Tools Centre provides SEO checker services for websites.
Keywords Everywhere - Free browser add-on for keyword volume, CPC & competition