Twitter Audience Insights - Loads of info about your followers, their interests, & more
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.
Owlead - Grow your Twitter with valuable followers, effortless
Google Trends - Explore Google trending search topics with Google Trends.
Retargetlinks - Turn every link you share into targeted ads
Keywords Everywhere - Free browser add-on for keyword volume, CPC & competition