DualBootPatcher is an open-source app that allows multiple ROMs to be installed on a single Android device. It does its best to work with existing code and does not require explicit support from ROMs. There are currently 210 supported devices and their variations.
Website: link XDA thread: link
Downloads can be found here.
See the docs/ directory for instructions on building for Linux, Windows, and Android.
The patcher is licensed under GPLv3+ (see the LICENSE file). Third party libraries and programs are used under their respective licenses. Copies of these licenses are in the licenses/ directory of this repository. Patches and other source code modifications to third party software are under the same license as the original software.