Writing a trivial
ffmpeg ClickStack is easy, and testing it directly on RUN@cloud with a demo application is fine. For more complex stacks, you'll need some way to test and diagnose them.
GenApp is an open source framework and is well documented at http://genapp-docs.cloudbees.com/. You can install a local GenApp to test your ClickStack plugins. As RUN@cloud's target environment is Arch Linux, it won't make much sense to give it a try if you don't use a Linux or an OS X system. Running on Windows using Cygwin may work, but it is not the best option.
Follow the Quick Start guide (http://genapp-docs.cloudbees.com/quickstart.html) to get an overview of the use of GenApp and ensure that everything is working fine ...