The stable PPA is indeed no longer being maintained.
The nightly PPA is being kept for development purposes and should not be used on any sort of production machine (it can and will break at any time).
To be honest, I don’t have an alternative to offer Ubuntu users at the moment, apart from switching to a distribution that does support Cinnamon. There are many such distributions out there, and I’m only hoping for someone to (finally) step up on Ubuntu’s side to provide proper packages to its users.
Gli utenti che vorranno provare Cinnamon su di Ubuntu 14.04 dovranno dunque rassegnarsi e aspettare magari un nuovo manteiner pronto ad accollarsi il repository. Source: MarcosBox