This method involves the use of an emulator such as QEMU to run a virtualized Linux environment inside a Windows or MacOS environment. This means there is no need to install Linux on a computer, and no need to dual boot.
This approach does not require constant Internet access, and is relatively efficient. Furthermore, the virtual machine can run on a variety of computers, and stored on a thumb drive or external hard drive.
The down side of this approach is that the host Windows or MacOS system must have reasonable computational resources, such as the amount of RAM and processing power. A Pentium 4 processor is a minimum for reasonable performance, although a Pentium III can still be used with lower performance. At least 1GB of RAM should be install on the computer, as the VM itself can consume at least 256MB.