keyword suggestion tool

Any idea about a free and good Keyword suggestion tool? A tool that I can feed seed keyword into it and it brings me all other related keywords. Don't care about keyword volume, nor difficulty. I tried this https://www.twinword.com/ideas/ And this https://app.getkeywords.io/login But they...

I don't have much experience of using this tool but it looks pretty good to me. How good this tools really is and is there a better option than this?