I wrote a few simple tweaks when I used an iPhone 4S. Since I have an iPhone SE now, these are very unlikely to be updated.
This tweak tries to fix connection issues by looping a silent MP3; it does help but I don't really understand why. Reddit post.
A workaround for random shutdowns in cold weather. This may degrade your phone's battery or cause data loss. Source code.
It hides the iOS 9 lock screen music controls until the home button is clicked, the opposite of the default behavior. Source code.
This tweak enables the volume keys to turn pages, an FBReader feature I missed from my Moto E4.