Keywordtool.io is an online keyword research tool that uses Google autocomplete feature to generate different long tail keywords. It is considered as the best alternative for Google keyword planner and Ubbersuggest as well. Like both the Google and Ubbersuggest, it also comes with free to use option loaded with thousands of long tail keyword suggestions per search.
Apart from that, this tool has amazed me with its lightening speed, accuracy and simple design. It reveals long keywords that Google AdWords hides from us, making a perfect tool for everyone. The most part of this tool what I liked is its ability to produce keywords for both websites and for mobile apps as well.