This post is a few weeks late, however JSApp.us has been shutdown. At the time that JSapp was first released, it was the first open node.js hosting platform. It featured an easy to use web based code editor (which was extremely useful at the time as developing node.js on windows was fairly difficult and required compiling code yourself). The system also provided CNAME support as well as subdomains for quickly developing demonstrating applications. There was even a command line client which allowed for quick deployments from the command and uploading and downloading files from ones file system.
Given the abundance of alternate Node.js hosting options and the age of the system, it seems that essentially all users have already migrated off the platform, so this change is unlikely to been disruptive. The source will remain available on github if anyone interested in some of the internals, however given how dated the system is, I am assuming that there are better solutions today for nearly all aspects of the system.