Open WordPress SEO
This is the open-source and free SEO Plugin For WordPress. The plugin is simple to use and packs all the important features.
You can find screenshots and more information at homepage.
Open WordPress SEO is a comprehensive tool for all your SEO needs.
View SEO status on dashboard
SEO toolbox in post edit
Analyzes your content and gives tips
Automation for routine actions
Actively developed in GitHub
Improved score in GTmetrix and Google PageSpeed Insights
…and many other features and benefits
By using Open WordPress SEO search engines find your pages more easily, index your posts faster, and rank your site higher.
You can contribute to development in GitHub.