Hypersomnia is a free and open-source multiplayer top-down shooter that has been online and playable since 2017. Written in modern C++ with no game engine, it blends the tactics of Counter-Strike, the frantic dynamics of Hotline Miami and the pixel-art nostalgia of old-school RPGs. Players declare allegiance to one of three factions — Metropolis, Atlantis and Resistance — and fight across arenas with 24 unique firearms, currently spanning two game modes: Bomb defusal and Gun game. A built-in map editor lets you playtest work-in-progress maps with friends instantly, and because the editor, game server and master server are all embedded in the same executable, anyone can host their own game — or their own community server list. Hypersomnia runs natively on Windows, macOS and Linux (including ARM) and also plays in the browser, with native and browser clients able to join the same servers. Development is active and community-driven, and the project’s stated goal is to become “the ultimate open-source shooter”.

Key Features

• Tactical top-down shooting — physics-based 2D combat with 24 firearms and a roster of community maps.
• Two game modes — Bomb defusal (Counter-Strike-style objective play) and Gun game, with ranked matches and global leaderboards.
• Three factions — Metropolis, Atlantis and Resistance, each with its own lore across the war-torn afterlife setting.
• Built-in map editor — design arenas and playtest a work-in-progress map with friends instantly, even behind a router.
• Cross-platform multiplayer — native Windows, macOS and Linux (aarch64 included) clients and browser clients play on the same servers.
• Deterministic networking — only player inputs are transmitted, so a duel costs roughly 5 KB/s at 60 Hz even with thousands of dynamic objects; bullet casings, fish and insects stay synchronised at no traffic cost.
• Host your own server — start a game server from the main menu (with automatic port forwarding) or run the dedicated / Docker server; the whole server infrastructure is open.
• Built-in self-updater — updates are applied automatically and verified against the developer’s signing key, so a compromised build host cannot push a malicious update.
• Tiny and lightweight — about 29 MB, launches straight into an interactive tutorial, and needs no game engine install.
• Free forever — no ads and no paywalls: the full game and its complete C++ source are free and open source.

Why Use Hypersomnia?

Hypersomnia is that rare thing: a genuinely competitive multiplayer shooter whose entire stack is open. The netcode is built on cross-platform simulation determinism so that physics-based play stays in sync across browser and native clients — a technique normally reserved for real-time strategy games — and it is documented in detail by its author. On top of that sit an in-game editor, self-hosted servers, ranked matchmaking and a signature verification scheme for updates. For players it is a fast, nostalgic pixel-art shooter that asks for nothing but your time; for developers it is an unusually well-documented study in deterministic networking, entity-component-system design and writing a game without an engine.

Use Cases

• Quick online 1v1 duels and larger clan wars.
• LAN parties and game nights, including on modest hardware.
• Designing, playtesting and sharing custom maps with the built-in editor.
• Running your own community game server — the server, editor and master server are all included.
• Studying real-time deterministic netcode, ECS architecture and modern C++ game programming.

Platforms

Windows · macOS · Linux (native, including ARM) · Web browser (also distributed on Steam)

Licence

Free and open source — GNU Affero General Public License v3.0 (AGPL-3.0).

Website

hypersomnia.io · play in the browser · source on GitHub

Similar open-source game

Teeworlds — another free and open-source 2D multiplayer shooter with a built-in map editor and self-hosted servers.