Limbo PC Emulator

Limbo is a front end for QEMU, the open-source machine emulator, packaged as an Android app. It emulates a complete x86 PC, processor, memory, disks, graphics, sound and network, so you can boot an operating system from an ISO or disk image inside it. It was written by Max Kastanas and is distributed through the project’s GitHub page, its site Virtual Machinery, and F-Droid.

It is no longer developed. The last release, 6.0.1, which its changelog calls “Limbo Legacy v6.0.1”, came out in March 2022 with QEMU 5.1.0 from 2020. The GitHub issue tracker is switched off and the wiki’s pages now only point to the Virtual Machinery site.

What it does

• Virtual machines with the CPU type and count, memory, hard disks, CD-ROM, floppy, network, sound and display you choose. A new machine starts with one CPU and 128 megabytes of memory.
• Empty disk images of 1 to 20 GB to install a system on, and since 6.0.1, a choice of disk interface and cache mode, and importing your own BIOS file.
• Display through its built-in SDL window or an external VNC viewer, which only listens on the phone itself unless you set a VNC password.
• A key mapper for keyboard keys and mouse buttons, added in version 6.0.0 for games.

What to expect

Limbo translates every x86 instruction in software. Even F-Droid’s description of it warns: “you most likely won’t be able to run modern operating systems with reasonable perfomance.” The project’s own site says Windows 7 “will be very slow to boot and operate”, and lists distributions such as Lubuntu as “too slow”. Lightweight systems like FreeDOS, KolibriOS and small Linux distributions are what it is suited for. Adding virtual CPUs “will NOT result in additional performance unless you use KVM or MTTCG”; KVM isn’t possible on an ARM phone emulating x86, and the multi-threaded mode is “not fully tested”.

Operating systems

Limbo ships with no operating system. After you create a machine, it offers links to guides for free systems, Slax, SliTaz, Damn Small Linux, Debian, Trinux, FreeDOS and KolibriOS, plus Custom for your own images; those links now land on the Virtual Machinery site. For Windows, that site says to “make sure you have a legitimate copy of your Windows operating system”, and points developers to the time-limited test machines Microsoft offers.

The firmware inside

Emulators that bundle a manufacturer’s BIOS aren’t something we host, so we listed every firmware file in this APK. All of them are free software: the PC BIOS and VGA BIOS are SeaBIOS, under the LGPL-3.0, which F-Droid rebuilt from source; the network-boot ROMs are iPXE, under the GPL; the rest are boot loaders from QEMU itself. There is no vendor firmware and no system image.

F-Droid’s build lacks a few prebuilt QEMU files that the GitHub APK includes, such as OpenBIOS, sgabios and the ROMs for booting a Linux kernel directly. Features that depend on them may not work in this build; we haven’t been able to test that.

What goes online

Nothing by itself. The update check is off by default. The emulated PC reaches the internet through the phone’s connection, using Google’s DNS server, 8.8.8.8, unless you change it in the settings. There are no analytics or crash-reporting libraries.

Before you install

• Old code. QEMU 5.1.0 has had no updates in this app since 2022.
• Newer phones. The app targets Android 10, which Android 14 and 15 still install. Its native libraries are aligned for 4-kilobyte memory pages; on phones that use 16-kilobyte pages, Android’s documentation says such apps may run in a compatibility mode, which “allows some apps to work”. We haven’t tested it.
• Where your machines live. Limbo keeps its working files, including saved machine states, in its cache folder, so clearing the app’s cache most likely deletes them. Keep your disk images somewhere you choose.

About this file

• This is F-Droid’s build of 6.0.1, the x86 edition (6.0.1-x86): it emulates a PC, and runs on ARM phones, 32- and 64-bit. Limbo’s separate ARM, PowerPC and SPARC editions are different apps that F-Droid doesn’t build. The site says to download Limbo “strictly from the Github release pages”; the GitHub APK is signed by the developer, this one by F-Droid, and neither can update the other.
• The 16.4 MB file runs on Android 5.0 and later and declares 11 permissions, for the virtual machine’s network, keeping Wi-Fi and the processor awake while a machine runs, storage, audio and vibration.
• Limbo is licensed under the GPL-2.0 or later. QEMU is a trademark of Fabrice Bellard.
• The project publishes no screenshots of the app.

CPU types in this build: arm64-v8a (64-bit ARM, almost every phone since 2017); armeabi-v7a (32-bit ARM, older and budget phones).

Versions currently kept in the F-Droid repository. We host and check only the newest one.