When comparing Duality vs GameMaker:Studio Marketplace, the Slant community recommends Duality for most people. In the question“What are the best 2D game engines?” Duality is ranked 29th while GameMaker:Studio Marketplace is ranked 74th. 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
Question 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 Has a selection of free assetts
About 30 free assets are available.
Pro Reasonably priced
Most assets are under $5. The more advanced assets can usually go for around $20-$25.
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 Can be used with Game Maker only
Assets are only offered to Game Maker developers.