When comparing Duality vs Flax Engine, the Slant community recommends Duality for most people. In the question“What are the best game engines?” Duality is ranked 9th while Flax Engine is ranked 12th. The most important reason people chose Duality is:
The full source code is available on GitHub, where the framework is actively developed. All of the editor, core and plugin code is written in C#.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Open source
The full source code is available on GitHub, where the framework is actively developed. All of the editor, core and plugin code is written in C#.
Pro Great editor
Duality includes a powerful visual editing system that can be used for previewing, integrating, editing and testing game content.
Pro Live reload of code and assets
Pro Very extensible
Because both Core and Editor are completely plugin-based, Duality not only incorporates a clean and modular design, but is also very extensible - even if it wasn't Open Source. In fact, most of the standard editing capabilities comes in form of Editor plugins.
Pro Built-in physics and lighting
Pro Friendly to version control systems
It can be configured to serialize all data in a text-based format, which has been structurally optimized for version control systems.
Pro Used in commercial projects
It has been used in a production environment without burning the place to the ground. Supposedly artist-proof editor workflow with an API for tailoring the system to fit your team.
Pro Free
Can be used for free until you hit a rather high revenue cap, at which point you have to pay royalties.
Pro Powerful C# scripting
C# scripting is really well made, comparable to Unity, but without any of the legacy cruft.
Pro Multiplatform
Supports most platforms, including Windows, Linux, Android, Nintendo Switch, ...
Pro Modern rendering backend
Has a very modern, performant and beautiful rendering backend.
Pro C++ support
The entire core is written in C++ and it supports writing game code in C++. The interoperability between C# and C++ is also nothing to scoff at.
Pro Supports multiple IDEs
Works with any text editor and comes with proper support for Visual Studio, VSCode and Jetbrains Rider.
Pro Excellent documentation
The documentation is well written, up to date and accepts improvements from the community.
Pro Great and extensible editor
The editor is both powerful and simple. My favourite part is how easy it is to extend the editor with custom magic.
Pro Source code available
The entire source of the engine is available on Github, though not under an open source license.
Cons
Con Visual Studio required
To have possibility for scripting you have to download entire Visual Studio and spend 10 GB of free space
Con Requires windows for development
Con New software
As is standard with new software, not all of the bugs have been ironed out yet.
Con Few plugins
Unlike more mature engines, there isn't a vibrant ecosystem of plugins yet.
Con Not open source
While the source code is available, it's not quite open source
Con Not latest C# version
It uses Mono and is still on some variant of C# 7.
Con No OpenGL support
It only supports modern APIs, namely Vulkan and DirectX. This means that it won't run on very old machines.