Is it possible to run Piwik as an app on PHPfog's free shared Cloud hosting?
There are several restricitons on PHPFog shared Cloud like 48MB Memory Limits or Disabled Functions like "file_get_contents for remote URLS". Look here for a full list: http://docs.phpfog.com/index.php/features/article/shared_vs_dedicated
Has somebody already tried this?
I checked Piwik a while ago actually. You can get it off the ground for sure but full functionality isn't available till you upgrade to a dedicated plan.
You may also want to try running a Piwik Amazon Machine Image directly using BitNami. If you combine it with the AWS free tier, you can get basically a free Piwik server (Disclaimer, I am one of the BitNami developers)