Xenu's Link Sleuth - Xenus Link Sleuth checks Web sites for broken links.
OpenSSL - OpenSSL is a free and open source software cryptography library that implements both the Secure Sockets Layer (SSL) and the Transport Layer Security (TLS) protocols, which are primarily used to provide secure communications between web browsers and …
LinkChecker - LinkChecker is a free, GPL licensed website validator.
Ensighten - Ensighten provides enterprise tag management solutions that enable businesses manage their websites more effectively.
Scrutiny - Scrutiny for Mac helps you manage and improve any number of websites. Link check, search, full website spell check, XML sitemap generator, SEO audit
Let's Encrypt - Let’s Encrypt is a free, automated, and open certificate authority brought to you by the Internet Security Research Group (ISRG).