The Screaming Frog SEO Spider is a small desktop program (PC or Mac) which crawls websites’ links, images, CSS, script and apps from an SEO perspective.
httpstatus.io – HTTP Status Code Checker.
Browseo.net – Your New SEO Browser. View any web page like search engines see it. Browseo helps you to identify issues with your site and with competitors’ sites. 100% free.
SEO Macroscope – Free and open source website broken link checker and Technical SEO toolbox for Windows.
Greenflare SEO Web Crawler. Open Source SEO Crawler and Analysis Tool for Windows, macOS and Linux.