FusionPen, created by the team at Punkt.de, makes it extremely easy to experiment with and try out smaller and bigger code examples independently from a given project.
You define your Fusion prototypes in FusionPen. The first found prototype is used for rendering - so this way, you can name the prototypes any way you like.
By clicking "share your code", the code is saved in the database and a unique link to the current code state is generated. Changing the code generates new links - this way, you can save different versions.
Additionally, FusionPen supports different CSS frameworks as well.
Core team member Marc Henry Schulz has built a web application that shows the transpiled fusion of an AFX snippet. This is helpful to diagnose how AFX transpiles to Fusion, and why 'x' wasn't working as expected.
Currently the converter uses the old deprecated RawArray (instead of Fusion:DataStructure) and Array (instead of Neos.Fusion:Join).