Holly Website Audit - Free, brandable website audit for your potential clients
Ahrefs Backlink Checker - With the world's biggest index of live backlinks (over 15 trillion), Ahrefs Backlink Checker will show you the most complete backlink profile for any website.
Website Grader - Grade your website's strengths and weaknesses in seconds.
Whatsmyserp - Powerful Rank & Serp Tracking. Completely Free.
Website Speed Ranker - Compare how fast your website loads vs your competitors
Backlink Tool - A backlink tool to index your links quickly and freely.