APPlyzer - Professional rankings & keywords for app developers, marketers and publishers.
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.
Sensor Tower - Sensor Tower is a platform for app store optimization and app industry intelligence.
Keyword Surfer - Get search volumes & keyword data directly in Google.
ASO by 2Stable - Find the most relevant keywords for your app
Keyword Explorer by Moz - Find the best keywords to improve your website's SEO traffic