I can personally attest that it is straightforward to port Linux-based web apps to work on Sandstorm. Over the weekend, I ported a game of mine. You can play an instance of it here (warning, makes sound): https://alpha.sandstorm.io/grain/ozfn8bSxa6Ygt74YA

If you have a Sandstorm server, you can install your own instance of this game by grabbing "Duoludo" from the Sandstorm "app store": http://sandstorm.io/apps