With limbo, you can emulate a complete desktop computer on your device and install various operating systems (FreeDOS, Windows, KolibriOS, various GNU/Linux distributions, and any other x86-compatible OS).
With Limbo, you can change RAM, the number of emulated cores, the type of CPU, mount hard-drive and CD-ROM images, select emulated graphics, network, and audio card types, and more.
F-Droid has clients for com.coboltforge.dontmind.multivnc, android.androidVNC, and com.coboltforge.dontmind.multivnc which enable access to the emulated desktop inside of limbo.
Android devices with x86-based CPUs (Intel Atom) can run Limbo in KVM mode, improving performance.
Since limbo emulates another CPU architecture, you probably won't be able to run modern operating systems with reasonable performance.