Free Instagram followers app is a mobile (about 80%) app through which users can boost followers count following each other. Many of such apps require not only downloads and installs of third-party software on your device, but connecting an app account to the Instagram page. This increases the risk of accounts being hacked, and personal data stolen.
Out of dozens of Android and iOS applications to get free followers without surveys, only few can really provide real followers. Most of them pretend they can send 1000 free Instagram followers while increasing the number of app downloads and installs to promote their software. Also, there is always a risk of getting bots instead of the real followers, and being suspended.
On the flip side, those apps which do send followers free, are likely to sign up real users who are there for the same reason as you - to follow and get followed.
Before we get into iOS or Android APK, let's briefly get into why app providers would offer a legit service for free. Developing an app costs money, and real Instagram followers have to be incentivised to follow other users. This makes you question how Instagram followers apps work and why hundreds of users are downloading them?