Flax Engine is a free, source-available C++/C# game engine led by developer Wojciech Figat. Free until $250k quarterly revenue, then a 4% royalty applies.
Flax Engine is a game engine with full editor and runtime source code access, originated in Poland in 2012 by developer Wojciech Figat and since grown through an active community of contributors. It supports building both 2D and 3D games with C++ and C# scripting, plus a visual scripting system for designers who prefer not to write code directly.
Unlike a purely community-run open-source project, Flax operates a licensing model similar to Unreal Engine's: the engine and its source code are free to use, including for commercial projects, up to a revenue threshold, after which a royalty applies rather than an upfront purchase price.
The engine is built around fast iteration, with its marketing emphasizing the removal of long import times, lagging editor actions, and slow compilation that can slow down other engines' workflows. Its editor is extensible, and projects can be tracked in standard version control systems rather than requiring proprietary project files.
Because the full editor and runtime source code is available, studios can modify core engine behavior directly rather than working only through exposed APIs, which is a common reason teams choose source-available engines like Flax, Unreal, or CryEngine over closed engines.
Flax is free to use for non-commercial and educational projects, and commercial projects can also use it for free up until they exceed $250,000 in revenue within a calendar quarter, at which point a 4% royalty applies on the amount above that threshold. This mirrors the royalty structure Unreal Engine popularized, rather than charging a flat license fee upfront.
For studios that prefer not to use the royalty model, Flax also offers custom licensing arrangements, including per-seat licenses billed monthly or annually, or a flat fee that can be scoped to a specific project.
Yes, Flax is free for non-commercial, educational, and commercial use up to $250,000 in revenue per calendar quarter; a 4% royalty applies to revenue above that threshold.
Flax was started by developer Wojciech Figat in 2012 and continues to be led by him along with a community of contributors.
Yes, the complete editor and runtime source code is available to all users, not gated behind a separate license tier.
Yes, custom licensing is available, including per-seat licenses billed monthly or annually, or a flat project-based fee.
Flax supports C++ and C# for code-based scripting, plus a visual scripting system for non-programmers.