- If you're looking for a paid one and inclined towards knowing more about competition, then Ahrefs. It's data-driven (much more than SEO) -they crawl 6 billion pages every day and you can learn almost everything about your competitors. It helps to know where your competition is getting traffic from, exact keywords they use, how much traffic it brings them and how many backlinks & who exactly links to their website. You can also set “Alerts” for website rankings or mentions.
- 4SEO Site CheckupThis one lets you scan your website once every few hours (if you don't want to pay), but it does it really well IMO. Simple, easy to implement outcomes.