• Use Ctrl + F or command + F to search for a module.
• Contributions are welcome.

HTML Form

• Contact Form 7 - It can manage multiple contact forms, plus you can customize the form and the mail contents flexibly with simple markup.
• WPForms - Drag & Drop WordPress Form Builder

Security

• Sucuri - Auditing, Malware Scanner and Security Hardening
• iThemes Security - iThemes Security (formerly Better WP Security) gives you over 30+ ways to secure and protect your WordPress site.

SEO

• Yoast SEO - Yoast SEO is the most complete WordPress SEO plugin. It handles the technical optimization of your site & assists with optimizing your content.

Caching

• W3 Total Cache - W3 Total Cache improves the SEO and user experience of your site by increasing website performance, reducing download times via features like content delivery network (CDN) integration.