SAI is an app for installing split APKs - apps that consist of multiple APKs. It has both rootless and rooted installation methods.
SAI is an open-source app, you can get the source code on its GitHub repo - github.com/Aefyr/SAI
Please note that SAI only installs user-provided files and is not responsible for those apps behavior.
Please also note, that some devices/ROMs aren't supported by SAI, that has to do with bad Android API implementation in said ROMs and can't be fixed on app side.