George Moschovitis, one of the developers of AppengineJS, said that all of this means that he wouldn't recommend any of the tools for serious production work because they're "too immature." But he adds quickly, "I would heartily recommend Node.js and others for prototypes and basic enterprise projects." He notes that projects like Harmony, CommonJS, and Node.js may "change this in the midterm."
In other words, these tools work well for basic prototypes. They're quick and relatively stable. If things go well, they may prove to be ready to add bits and pieces of real responsibility to the programs. When that happens, the projects will slow down and the feature sets will begin to freeze as the users start demanding stability and bug fixes over experimentation and innovation.