GRUB - Multiboot boot loader
QEMU - QEMU (short for "Quick EMUlator") is a free and open-source hosted hypervisor that...
EasyUEFI - Manage EFI/UEFI Boot Options & Manage EFI System Partitions & Fix EFI/UEFI Boot Issues
Portable Virtualbox - Portable-VirtualBox is a free and open source software tool that lets you run any operating system from a usb stick without separate installation. Installation instructions. Download and run Portable-VirtualBox_v5.
EasyBCD - EasyBCD is NeoSmart Technologies multiple award-winning answer to tweaking Windows bootloader.
bochs - Bochs IA-32 Emulator provides a virtual PC that can run operating systems such as Windows, Linux, and BSD.