Android Boot Manager is a new dualboot tool for Android. There were many of them before, such as: EFIDroid, MultiROM, Dualboot patcher, etc. Usually they reflashed boot dynamically for dualbooting. Some of them used one big hack like MultiROM's kexec-hardboot.
Android Boot Manager uses lk based bootloader flashed to boot partition for loading the device tree, kernel and ramdisk, and an android app with sh scripts and pre-compiled binary for easy rom management.In some rear cases (such as yggdrasil) Android Boot Manager's bootloader is flashed instead of stock.
For now project is in pre-alpha stage. Actively developed.
For now this is developed for Motorola Moto G5 (cedric) and Volla Phone(yggdrasil), but a bit later I will create a porting guide.