I've also been approached by a number of clients with a very similar request. I work out of Hollywood, so its actually something like 1 out of 5 startups have this model... Just saying..
I targeted Linux (or Linux like) users: Ubuntu, Fedora, Android. I leveraged existing working and well tested infrastructure used in Linux. It is simple and working well (for Linux users), but I have no money to push it forward any more...