Microsoft has released the eighth major version of its Remote Desktop app which essentially puts Windows 8 on your iPhone or iPad.
Available as a free download from the iTunes App Store, Microsoft Remote Desktop 8.0.0 lets you connect to a remote PC and “Experience the power of Windows with RemoteFX in a Remote Desktop client designed to help you get your work done wherever you are.”
Key features include: the ability to access to remote resources through the Remote Desktop Gateway, a rich multi-touch experience with remote desktop protocol (RDP), Windows gesture support via RemoteFX, security ensured by Network Layer Authentication (NLA) technology, remote connections management, improved compression and bandwidth usage leading to higher-quality video and sound streaming, support for external monitors or projectors.
The software calls for iOS 6.0 and a compatible device. No restrictions are mentioned, meaning even an iPhone 3GS should work (though I seriously doubt it would). Download Microsoft Remote Desktop for iOS (Free)