Online co-op for Fallout 4 - by FatherLamb (YouTube: FatherLamb)
Play Fallout 4 together: each player uses their own character and save, and everyone shares the host's world - NPCs, enemies, quests, settlements, loot, doors and builds.
Alpha. Expect bugs and back up your saves (
Documents\My Games\Fallout4\Saves) before playing.
Get the latest build from the Releases page. Unzip it, run
FathersFallout.exe and follow README - START HERE.txt - it covers installing, hosting,
joining through Steam (no IP needed) or by IP (GOG), known issues and how to report bugs.
Requirements: Fallout 4 1.11.240 with all 6 DLC, plus three free tools from their own authors: F4SE, Address Library for F4SE Plugins and F4SE Menu Framework (the launcher checks for them and links to each).
- Player guide - install, host, join through Steam or by IP, in-game menu
- Known issues & what's being worked on
- FAQ - is it safe, Windows warnings, saves, mods, Steam join problems
The launcher isn't signed with a paid certificate, so Windows SmartScreen may say "Windows protected your PC" - click More info → Run anyway. All the code is right here to read, each release lists SHA-256 checksums so you can check your download, and the FAQ lists exactly what the launcher touches.
Right after playing, press [ SHARE LOG ] in the launcher: it saves your co-op log to the Desktop with personal details (IP addresses, Steam IDs, your Windows user name) removed and opens the bug report form - drag the file in. Logs from both players help the most.
Movement and animations, weapons and armor (with their mods), power armor, sitting and lying on furniture (players and NPCs, including NPCs cooking or eating at a campfire), NPC idle animations, shooting and melee - aimed where each player really aims - damage (including between players), enemies and NPCs, deaths, explosions, doors and switches, dropped items, containers, building / moving / scrapping in workshops, power wires, settlers' jobs, quest progress (every stage, from the host and the guests), time of day and weather. Plus proximity voice chat: hold N to talk to the players around you.
The source is here as the GPL requires. You don't need it to play - use the Releases.
| Part | Folder | Build |
|---|---|---|
| Game plugin (F4SE DLL) | client-ng/ |
xmake: cd client-ng && xmake (uses CommonLibF4, a git submodule: clone with --recursive) |
| Co-op server | server/ |
setup_deps.bat once (builds GameNetworkingSockets, spdlog... with vcpkg), then build_server.bat |
| Launcher | tools/launcher/ |
build.bat (the .NET Framework compiler that ships with Windows) |
Requires Visual Studio 2022 with the C++ desktop workload.
FathersFallout - Copyright (C) 2026 FatherLamb.
The code is free software under the GNU GPL v3 with additional terms (GPL section 7) - see LICENSE and NOTICE. In short: keep the credits, and a modified version must be clearly marked as modified and must not use the names "FathersFallout" or "FatherLamb".
The logo, icon and other artwork in tools/launcher/art/ are not covered by the GPL and may
not be reused without permission (see tools/launcher/art/README.txt).
- F4MP - Copyright (C) 2020 Alin Octavian, Benjamin Kyd (GPL v3): the original server and design.
- Jous99's F4MP rework (public domain).
- CommonLibF4 (GPL v3), Valve's GameNetworkingSockets (BSD 3-Clause), Protocol Buffers, Abseil, OpenSSL, spdlog, fmt, nlohmann/json, Dear ImGui (via F4SE Menu Framework).
- Steam joining uses Valve's Steam networking through the game's own Steam client.
Fallout 4 is a trademark of Bethesda Softworks LLC. FathersFallout is a free fan-made mod, not affiliated with or endorsed by Bethesda Softworks or ZeniMax Media.