What is the best free SEO tools?

Website Crawler – http://beamusup.com/

SEO & Website Analysis – https://www.woorank.com

SEO Audit Tool – https://seositecheckup.com/

SEO Performance Report – https://www.google.com/webmasters/tools/

Keyword Rank Tracker – https://seopoz.com/

Visitors Analytics – https://www.google.com/analytics/

Keyword Search Volume Tool – https://searchvolume.io/

Page Speed Tool – https://developers.google.com/speed/pagespeed/insights/

Backlink Checker – https://www.seoreviewtools.com/valuable-backlinks-checker/

Backlink Analysis Tool – https://www.openlinkprofiler.org/

Serp Checker – https://serpyou.com/tools/serp-checker