MoodSwings
An open-source comedy sandbox game in Rust and Bevy, set in a city where moods spread from person to person.
MoodSwings – Die Stadt der Flummis is an open-world comedy sandbox game I am developing. Unlike my other projects, it is not a photography tool. In the game’s city, people and cars bounce, and moods spread from one resident to the next. The game is open source and written in Rust with the Bevy engine. The source code is on GitHub.
How moods spread
Every resident has a temperament and a mood. You can see it in their face and hear it in their reactions. Taunting, for example blowing a raspberry, makes people cross. Whistling or cheering someone up lifts their mood. Bumps count too: a gentle nudge can come across as a joke, a hard collision as an insult.
Some residents shrug it off. Others hold a grudge and bounce after you. A collision can upset the next person, who passes the mood on again. You can throw a flower to apologise. The same rules apply to everyone in the crowd, so moods also spread without your involvement.
There are no weapons, health bars or failure state. You explore, drive, provoke people, make peace and watch the reactions. Optional Stadtmomente give an outing some direction, for example a walk, cheering up different residents or spending time near street music. They have no countdown and no penalty.
Landshüpf and other city styles
The Landshüpf city variant is a playful version of Landshut. Its streets use map data © OpenStreetMap contributors, the building footprints come from Overture Maps and the terrain from Copernicus elevation data. The Altstadt, the Isar and the hills around the town shape the map. The picture at the top of this page is a screenshot of Landshüpf from the development version, taken in September 2026.
Other city styles, including New Dork, Londoof, Minga and Paree, are procedurally generated; each style adjusts the city generator. The game has weather and a day/night cycle, and pedestrians and traffic move through the streets.
The same town at night.
Tech stack and licence
MoodSwings is written in Rust and uses the Bevy game engine and Avian 3D for physics. City generation, the elastic movement, the character expressions and the mood simulation are all part of the source code. The project is licensed under GPL-3.0-or-later. Credits for assets and map data are listed separately in the project credits.
You can play with keyboard and mouse or with a gamepad. Menus and HUD are in German; the development documentation is in English.
Multiplayer (experimental)
An experimental multiplayer mode lets up to 16 players explore the city together on foot. It requires matching game revisions and a dedicated server. The server is intended for a trusted LAN or a private VPN. Multiplayer is more limited than solo play: you cannot get into vehicles, and save/load is disabled. The multiplayer documentation explains the setup and the current limitations.
Build and play
Status on 13 September 2026: the source code is public and you can build the game locally. There are no packaged releases on GitHub yet. The project is still in development: expect rough edges and features that may change.
Start with the README and build instructions. You need the Rust toolchain and the project’s asset setup. For audio, you also need the sound-bank download. Check the repository for the current requirements; this page is an overview, not a version-specific installation guide.
If you notice something odd or have an idea for the city, open an issue or read the contribution guide.
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