Nibbler is a free tool for testing websites. Enter the address of any website and Nibbler will give you a report scoring the website out of 10 for key areas, including accessibility, SEO, social media and technology.
Nibbler is completely free, but limited to three reports.
WP Checkup - Get a WordPress Checkup Quick, Free & Easy | WPMU DEV
SiteCheck scanner will check the website for known malware, blacklisting status, website errors, and out-of-date software.
Free External Risk Assessment
Test Malware! - WICAR.org - Test Your Anti-Malware Solution!