We switched to Nightwatch from Stat after some issues and realizing they support wide range of functionalities with have a more friendly interface. Happy so far!
Moz - Backed by industry-leading data and the largest community of SEOs on the planet, Moz builds tools that make inbound marketing easy.
Monitor Backlinks - Easy Link Management - SEO Tool for automatically checking your backlinks.
Serpstat - Search analytics, Rank tracking, Backlink analysis and Site Audit tool.
Topvisor - All in one SEO and PPC tools for better marketing.
SEO Tools Centre - SEO Tools Centre provides SEO checker services for websites.
Botify - Traffic Managers, SEO Managers, Webmasters:Crawl your site to extract all of its metadata and identify areas for improvement