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' wasnt working as expected.