Alternatively, if your application is much more about processes, and data isn't as important, or isn't as relational, Node.js might be a better thing to develop in it. The main problem with Node at the moment however is that it's much less mature than the Rails/Ruby community, and lacks the higher level frameworks like Rails.
I can't recommend PHP for anything at all, unless you've got 10 years PHP experience and don't want to learn a new technology. Although I'm guessing that isn't the case from the wording of your question.
Some other things you might want to consider: Python and Django are similar to Ruby/Rails. I think Rails is a bit more capable, but Django is easier to learn. C# and Microsoft's MVC stack is remarkably good - I usually don't work with anything Microsoft based, but was given a project that required it, I was very impressed.
Also, I can’t speak for PHP but there aren’t any frameworks for Node that does nearly as much as Rails does (Sails[1] being the closest, but yet still far)
Though personally I won't work with it unless it's running Twig for templates. To each their own, though.
2. It has also proven to be faster and more smoothly scalable than Ruby on Rails.
3. You'll find a good community support and lot, a lot of modules for nearly any purpose you seek in your application.
4. Many industries are moving to use it (Microsoft, LinkedIn, PayPal, NYTimes ... )
Also, as long as you're looking at all those options, don't forget about Python/Django.
It really comes down to what you know best, what you can get other developers for the easiest, and what is most easily maintained over the long term.
But that's only a 'possibility,' we don't know you personally so we can't judge how determined you are to achieve your goals no matter what.