LinkChecker - LinkChecker is a free, GPL licensed website validator.
ServerSuit - ServerSuit is a browser based program that enables remote Linux administration, monitoring, website hosting, and server setup automation.
DRKSpiderJava - DRKSpider is an open source website crawler (sitemap generator) and link checker. Features:
Netumo - Ensure healthy website performance, uptime, and free from vulnerabilities. Automatic checks for SSL Certificates, domains and monitor issues with your websites all from one console and get instant notifications on any issues.
Pulno - SEO Audit and Website Analysis. Pull up your SEO.
AppZero - AppZero is a monitoring and migration tool that allows users to keep track of different applications and servers in both simple and complex IT environments.