Something similar I've been using: http://webappkit.org
"WebAppKit is a BSD-licensed framework for creating web applications using Cocoa and Objective-C, running on Mac OS X."
Quite neat to use Obj-C and all the great frameworks on the web as well.
The big problem with using Objective-C for stuff like this is that you almost have to host it on Apple Hardware, which is quite expensive and hard to do by your self in a cloud-like fashion. With the Objective-C in the cloud service you move the hosting to them of course, but it is still a problem lurking when (and if) they are going to scale it really big.
As someone who has used both GNUStep and Cocotron, I have to say this is less true than you probably think, and yes, there are people actually doing it.
In fact, one of my recent gigs was moving an Objective-C code-base from GNUStep/Linux to Mac OS X (and then with Cocotron back to Linux).
Objective-Cloud seems to be a perfect bridge between those worlds. After all: worry about scaling problems once you scale, because chances are you won't ;-)
And if you do scale up so amazingly that you outgrow Objective-Cloud or hosting your own, I am pretty certain that the transition will be less involved/painful/drawn-out than, let's say, Twitters move from Rails to Java. :)
Well, technically it doesn't have to be Apple hardware. They could be running hackintoshes, which would obviously be against the EULA of OSX. Another possibility is virtualization. Somebody correct me if I'm wrong but I think the OSX Server EULA allows virtualization since 10.7. So setup any linux server off the shelf and virtualize OSX Server instances on it and you have your cloud building blocks.
The Apple Software License Agreement for OS X Mountain Lion[1] is not your friend here.
…you are granted a limited, non-transferable, non-exclusive license:… (iii) to install, use and run up to two (2) additional copies or instances of the Apple Software within virtual operating system environments on each Mac Computer you own or control that is already running the Apple Software, for purposes of: (a) software development; (b) testing during software development; (c) using OS X Server; or (d) personal, non-commercial use.
So development, testing, running OS X Server, and non-commercial are the legal uses.
The Mac OS Server license is more restrictive, a single copy on Apple branded hardware.
The license does allow virtualization, but only on Apple hardware running Lion or later as the host OS. So there's still no way to run OS X on commodity hardware without violating the EULA.
There's opensource Obj-C compilers by both GNU and LLVM/Clang available for windows and linux, so it doesn't have to be hosted on apple hardware afaik, but when you start using library frameworks, that I'm not sure about.
Quite neat to use Obj-C and all the great frameworks on the web as well.
The big problem with using Objective-C for stuff like this is that you almost have to host it on Apple Hardware, which is quite expensive and hard to do by your self in a cloud-like fashion. With the Objective-C in the cloud service you move the hosting to them of course, but it is still a problem lurking when (and if) they are going to scale it really big.