A browser DOS prompt that boots emulators from numbered menus, with bundled ROMs. Drop into a fake AMIBIOS POST, get a C:\> cursor, type a number, play a game. Everything runs on the page — no server, no network calls at runtime. Try it here.
We bundle 19 emulator engines covering 33 sub-systems between them, from the Apple I to the Sega Master System.
Scope: 8-bit feel — anything with the look and sound of an 8-bit machine (sprite-based, chiptune, low-res), including the 8-bit-feel handhelds (Game Boy/GBC, Game Gear, Lynx) even where they run into the late 90s. The cutoff is the aesthetic, not the calendar or strict CPU width; 16-bit home consoles/computers (Genesis, SNES, Amiga, ST) stay out. See the Roadmap for what's shipped, planned, and rejected.
./serve.shOr directly:
python3 -m http.server 8765Open http://127.0.0.1:8765/prompt/.
GenX-DOS is also published as GitHub Packages — the whole site bundled with its dependencies, no clone required.
Container image (the site served by nginx):
docker run --rm -p 8080:80 ghcr.io/retro-jack/genx-dos:latestThen open http://127.0.0.1:8080/.
npm package (the static site as files, to self-host or embed):
npm install @retro-jack/genx-dos --registry=https://npm.pkg.github.comconst express = require('express');
const genxdos = require('@retro-jack/genx-dos');
express().use(express.static(genxdos.path)).listen(8080);
// open http://127.0.0.1:8080/Both are rebuilt and published automatically on every GitHub Release (see .github/workflows/publish-package.yml).
index.html fake BIOS POST screen, redirects to prompt/
serve.sh starts the local server
CHANGELOG.md release notes
ATTRIBUTION.md canonical record of every bundled third-party asset
LICENSE.TXT CC BY-NC 4.0 for the original work (third-party excluded)
SECURITY.md scope + private vulnerability reporting
CONTRIBUTING.md local setup + PR ground rules; CODE_OF_CONDUCT.md alongside
package.json / index.js the npm package; Dockerfile builds the ghcr container
docs/ tech article + README screenshots + social preview
prompt/ the DOS terminal (HTML + JS, no build)
index.html
javascript/ terminal logic + virtual filesystem (fs.js)
img/ bitmap font sprite sheets + AMIBIOS logo
gamedocs/ per-game instruction pages (gamedocs/<platform>/<key>.html)
systems/
_shared/ shared CSS + helpers (NumLock warn, VICE RUN/STOP key remap, BBC COPY button, save-state, ...)
_shared-ejs/ shared EmulatorJS framework + 4 VICE cores + gearcoleco + FCEUmm + Stella + gambatte + handy + genesis_plus_gx + prosystem
(14 bundles share one ~3 MB framework; saves ~25 MB vs per-bundle copies)
apple1/ Apple I — apple1js + 10 cassette tapes
bbcmicro/ BBC Micro — jsbeeb Vite dist (Model B) + BBC disks
bbcmaster/ BBC Master 128 — jsbeeb Vite dist (model=Master) + Master-enhanced disks
electron/ Acorn Electron — ElkJS + 6 UEF snapshots
apple2/ Apple ][+ — apple2js webpack dist + 10 .dsk images
jsnes/ NES — EmulatorJS + FCEUmm + 10 .nes ROMs
stella/ Atari 2600 — EmulatorJS + Stella (stella2014) + 10 .a26 ROMs
gbc/ Game Boy / GBC — EmulatorJS + gambatte + 10 GB/GBC ROMs (handheld)
lynx/ Atari Lynx — EmulatorJS + handy + boot ROM + 10 .lnx ROMs (handheld)
gamegear/ Sega Game Gear — EmulatorJS + genesis_plus_gx + 10 .gg ROMs (handheld)
js7800/ Atari 7800 — EmulatorJS + ProSystem + 10 .a78 carts
msx1/ MSX1 — WebMSX 6.0 (stock wmsx.js + wrapper) + 10 titles
msx2/ MSX2 — WebMSX 6.0 (stock wmsx.js + wrapper) + 10 titles
sms/ Sega Master System — EmulatorJS + genesis_plus_gx + 10 .sms carts
jsspeccy/ Sinclair Spectrum — JSSpeccy 3.2 + 10 .z80 snapshots
jtyone/ Sinclair ZX81 — JtyOne + 10 .p tapes
xroar/ Tandy CoCo — XRoar WASM + 10 .ccc carts
trs80/ Tandy TRS-80 Model I — sdltrs built from source to WASM + 10 .cmd games
m100/ Tandy Model 100 — VirtualT core extracted to WASM + 10 .ba games (portable)
js99er/ TI-99/4A — vanilla-JS js99er + 10 .rpk carts
atari400/ Atari 400 — atari800 WASM, boots OS-B
atari800/ Atari 800XL — atari800 WASM, boots OS-XL
pet/ Commodore PET — Thomas Skibo's pet2001 (vanilla JS) + 10 .prg
vic20/ Commodore VIC-20 — EmulatorJS + VICE xvic + 10 cart .prg
max/ Commodore MAX — EmulatorJS + VICE x64 in Ultimax mode + 10 .crt
c64/ Commodore 64 — EmulatorJS + VICE x64 + 10 .d64
c16/ Commodore 16 — EmulatorJS + VICE xplus4 C16 mode + 10 .prg
plus4/ Commodore Plus/4 — EmulatorJS + VICE xplus4 + 10 .prg
c128/ Commodore 128 — EmulatorJS + VICE x128 native mode + 10 titles
coleco/ ColecoVision — EmulatorJS + gearcoleco + 10 launch-era .col carts
intv/ Mattel Intellivision — jzIntv WASM (custom loader) + 10 carts
cpc/ Amstrad CPC — floooh tiny8bit CPC WASM + 10 .dsk titles
odyssey2/ Magnavox Odyssey² — libretro-o2em + custom SDL2 frontend + 10 carts
The hand-written GenX-DOS code lives in prompt/javascript/, systems/_shared/, systems/_shared-ejs/, each emulator's play.html wrapper, and systems/m100/src/ (the Model 100's headless VirtualT build units + recipe) — all formatted for reading.
Everything else under systems/<name>/ is upstream: emscripten WASM glue (xroar.js, atari800.js, o2em.js, jzintv.js), webpack production bundles (apple1.js, apple2/dist/*.bundle.js, jsspeccy.js), the stock WebMSX engine (msx1/wmsx.js, msx2/wmsx.js), or hand-written JS from the upstream project (ElkJS, js99er's emu/). For the readable source of those, follow the upstream link in ATTRIBUTION.md or the per-engine integration story on the wiki.
Each engine has its own story page on the wiki — the gotchas we hit, the workarounds we shipped, the dead ends we ruled out. The table below is the quick-reference; click through to Emulators for the index.
| System | Copied from | URL pattern |
|---|---|---|
| Apple I | scullin/apple1js | play.html?tape=<key> |
| BBC Micro | mattgodbolt/jsbeeb | ?disc1=<path>.ssd&autoboot |
| BBC Master | mattgodbolt/jsbeeb (same build) | ?model=Master&disc1=<path>.ssd&autoboot |
| Acorn Electron | dmcoles/elkjs | play.html?game=<key> |
| Apple ][+ | whscullin/apple2js | play.html?game=<key> |
| NES | EmulatorJS + FCEUmm libretro core | play.html?game=<key> |
| 2600 | EmulatorJS + Stella (stella2014 core) | play.html?game=<key> |
| 7800 | EmulatorJS + ProSystem (prosystem core) | play.html?game=<key> |
| MSX1 / MSX2 | ppeccin/WebMSX (split into msx1/ + msx2/ bundles) |
?ROM=games/<name>.zip&M=MSX1 | &M=MSX2 |
| Spectrum | gasman/JSSpeccy 3 | play.html?game=<key> |
| ZX81 | JtyOne | play.html?game=<key> |
| Tandy CoCo | Ciaran Anscomb/XRoar | play.html?game=<key> |
| TRS-80 Model I | jengun/sdltrs (our own WASM build) | play.html?game=<key> |
| Model 100 | Hurd & Pettit/VirtualT (our own core-only WASM build) | play.html?game=<key> |
| TI-99/4A | Rasmus-M/js99er (vanilla-JS build) | play.html?game=<key> |
| Atari 400 / 800XL | atari800/atari800 (our own WASM build; split into atari400/ + atari800/ bundles) |
play.html?game=<key> |
| VIC-20 / MAX / C64 / C16 / Plus/4 / C128 | EmulatorJS + VICE libretro family | play.html?game=<key> |
| PET | Thomas Skibo's pet2001 (vanilla JS) | play.html?game=<key> |
| ColecoVision | EmulatorJS + gearcoleco (Drhelius) libretro | play.html?game=<key> |
| Intellivision | jzIntv (Joe Zbiciak) WASM, custom emscripten loader | play.html?game=<key> |
| Amstrad CPC | floooh/chips-test tiny8bit CPC WASM (Andre Weissflog) | play.html?game=<key> (rewrites to ?file=&input= for sokol_args) |
| Magnavox Odyssey² | libretro/libretro-o2em + custom SDL2/emscripten frontend | play.html?game=<key> |
ROMs are bundled locally — nothing is fetched at runtime.
The six VICE-family bundles (VIC-20, MAX, C64, C16, Plus/4, C128) share a unified input config (keyboardInput enabled + vice_joyport_type='1' Numpad) so typing and joystick coexist. Numpad 8/4/6/2 = joystick directions, 0/5 = fire, everything else types. Esc is browser-captured (exits pointer-lock/fullscreen) so we remap RUN/STOP to Scroll Lock + Pause/Break via systems/_shared/genx-vice-softkeys.js (RESTORE stays on the libretro default Page Up). The PET sits separately on Thomas Skibo's pet2001 (vanilla JS, BSD-2-Clause) — keyboard-only and unrelated to the VICE plumbing; see the wiki for the migration story.
The BBC bundles (jsbeeb) add a top-left COPY button via systems/_shared/genx-bbc-copykey.js — the BBC COPY key maps to the PC End key, which isn't obvious, so titles that use it (as an in-game "continue" or action key) get a click target. The TRS-80 Model I (sdltrs) likewise adds a CLEAR button via systems/_shared/genx-trs80-softkeys.js.
The EmulatorJS bundles read pads natively through the libretro cores. For standalone engines with no Gamepad API of their own, systems/_shared/genx-gamepad-keys.js polls pad 0 and synthesizes the keyboard events the engine already understands, driven by a per-game window.GenXGamepadMap (axes + button-index → key) defined in the bundle's play page — so each game's pad layout presses that game's own verified keys. The pad is gameplay-only — a game's title/start stays on the keyboard. Currently wired: Amstrad CPC, Acorn Electron, ZX Spectrum and the ZX81's action games (the ZX81 pages also filter out keys with no in-game function, since a stray Space is BREAK on that machine). Axis presses use hysteresis (on at 0.5, off at 0.3) so a hovering stick can't machine-gun key events, an idle pad sends nothing, and ?paddebug on any wired play page shows a live log of what the shim is sending.
Most bundles carry save / load controls in the bottom-left corner — each opens a drop-up menu of five save slots per game, an instant in-browser snapshot of the running machine kept in memory and persisted to IndexedDB (gx-savestate, keyed platform:game:slot) so the slots survive a reload. Because they're keyed per game, different games keep independent saves. The 14 EmulatorJS bundles use the libretro cores' own state API (systems/_shared/genx-savestate.js); the standalone engines that expose a reachable save-state — TI-99/4A, BBC Micro/Master (mid-game, even Elite), MSX, Tandy CoCo, Odyssey², Atari 400/800XL and Amstrad CPC — ride each emulator's native API through systems/_shared/genx-savestate-std.js + a small per-bundle GenXStateAdapter. Three needed a WASM rebuild to expose state the stock build hid: the Odyssey² (o2em — call libretro's dead-code-eliminated retro_serialize/retro_unserialize), the Atari 400/800XL (atari800 fork — StateSav_*, deferred through the frame loop to dodge an ASYNCIFY clash) and the Amstrad CPC (tiny8bit — export chips' cpc_save_snapshot/cpc_load_snapshot). The remaining engines (Apple, Electron, Spectrum, ZX81, Intellivision, PET) expose no reachable state API, so those bundles have no buttons. The TRS-80 Model I (sdltrs) ships a built-in save-state (trs_state_save/trs_state_load) that isn't wired to buttons yet — so no buttons there either, for now.
See the wiki for the long form. Each engine's integration story is its own page.
Prefer a narrative read? Booting a Museum in a Browser Tab is a magazine-style feature on the project — the concept, the static/no-build constraint, the emulator war stories, and the curation philosophy.
- Project Overview — what the site does and how it's structured
- Virtual Filesystem — the simulated
C:drive and menu layout - Commands — the DOS commands the prompt understands
- Font System — how we draw the 12×12 CP437 glyphs
- Emulators — index of every engine, each with its own page
- Customising the Filesystem — adding entries, batches, menus
The full licence text is in LICENSE.TXT, and ATTRIBUTION.md is the canonical record of every bundled third-party component (source URLs, authors, BIOS/ROM provenance, bezel artwork licences, and BY-SA share-alike obligations). Summary below.
- DOS terminal, virtual filesystem, and 12×12 CP437 font sprite system by Mike, written informally for LGR — Lazy Game Reviews (Clint Basinger, https://www.lazygamereviews.com)
- AMIBIOS POST animation, emulator integration wrappers, menu tree, and bundled-emulator-specific code by Retro-Jack
- jsbeeb: GPL-3.0-or-later (mattgodbolt/jsbeeb)
- ElkJS: (c) Darren Coles 2013 (dmcoles/elkjs) — 6502 core ported from Elkulator by Tom Walker
- apple2js: MIT (whscullin/apple2js)
- FCEUmm: GPL-2.0 (libretro NES core) — mirrored from
cdn.emulatorjs.org/stable/ - Stella: GPL-2.0 (
stella2014libretro core, stella-emu) — Atari 2600; mirrored fromcdn.emulatorjs.org/stable/ - ProSystem: GPL-2.0 (
prosystemlibretro core, stella-emu/libretro — Atari 7800) — mirrored fromcdn.emulatorjs.org/stable/ - WebMSX: MIT (ppeccin/WebMSX, Paulo Peccin)
- JSSpeccy 3: GPL-3.0 (Matt Westcott / gasman)
- JtyOne: GPL-2.0 (Simon Holdsworth, port of Mike Wynne's EightyOne)
- XRoar: GPL-3.0+ (Ciaran Anscomb)
- sdltrs: BSD-2-Clause (Mark Grebe / Jens Guenther, gitlab.com/jengun/sdltrs) — TRS-80 Model I, built from source to WASM; Model I Level II BASIC ROM (©Tandy/Microsoft) embedded for emulation
- Js99'er: GPL-2.0 (Rasmus Moustgaard) — vanilla-JS build
- atari800: GPL-2.0+ (atari800/atari800 v5.2.0, built from source to WASM); AltirraOS-XL/800/BASIC (Avery Lee, freely redistributable open-source OS replacement) embedded inside
atari800.wasmat build time via--enable-altirra_bios— no separate ROM file ships - EmulatorJS: GPL-3.0 (EmulatorJS/EmulatorJS) — modern fork of emularity; shared across 14 bundles via
systems/_shared-ejs/— the six VICE-family bundles, ColecoVision, NES, Atari 2600, Atari 7800, Sega Master System, and the three handhelds (Game Boy/GBC, Lynx, Game Gear) - VICE: GPL-2.0 (vice-emu.sourceforge.net) — libretro cores (
x64,x128,xvic,xplus4) mirrored fromcdn.emulatorjs.org/stable/ - pet2001: BSD-2-Clause (Thomas Skibo) — vanilla-JS PET 2001 emulator at
systems/pet/pet2001/ - gearcoleco: GPL-3.0 (Drhelius) — libretro ColecoVision core mirrored from
cdn.emulatorjs.org/stable/ - ColecoVision BIOS: ©1982 Coleco, bundled for emulator-only use
- jzIntv: Joe Zbiciak (free-for-personal-use terms) — WASM build mirrored from mholzinger/intellivision-overlay-editor
- Intellivision EXEC + GROM BIOS: ©1979 Mattel Electronics, bundled for emulator-only use
- floooh/chips-test tiny8bit CPC WASM: MIT (Andre Weissflog) — locally rebuilt from source (overlays patched out + save-state wrappers; see
systems/cpc/BUILDING-WASM.md) - libretro-o2em: GPL-2.0+ (libretro/libretro-o2em, original o2em by Daniel Boris / Andre de la Rocha) — compiled from upstream source via
systems/odyssey2/build.sh - Magnavox Odyssey² BIOS (
o2rom.bin): ©1978 Magnavox/Philips, bundled for emulator-only use
The original orchestration code, menu trees, and AMIBIOS POST animations authored by Jack Horton are licensed under Creative Commons Attribution-NonCommercial 4.0 International — see LICENSE.TXT for the full terms.
Please note that GenX-DOS is a composite project containing bundled emulators, assets, and the LGR terminal base framework. These components are explicitly excluded from the CC license and remain bound by their original upstream terms. See ATTRIBUTION.md for full compliance details.