I really like the Snoopreport Instagram activity tracker. However, as you understand from the name, it works exclusively for Instagram and this is its main disadvantage.
With it, you can monitor the activity of any IG users with a public profile. The tool will provide you with weekly reports with all the data: likes, hashtags, follows and interests. Further use depends only on your imagination and tasks. Personally, I most often track the activity of my current and potential followers, as well as the followers of competitors. I use the data obtained to select niche hashtags; create a content strategy; select influencers with anaudience brand match.