The Unity team have released a beta version of Unity 4.6 featuring a glimpse into the new UI system to be integrated into the game engine.
The 4.6 release gives developers an early hands on experience with the new UI system. Unity have announced "Unity UI is our new system for building UIs for multiplatform games and interactive content." and go on to add "It still needs polish, but already you’ll experience how efficiently you can create a UI for your content.".
A built in UI design system is a feature that was previously lacking from Unity and is commonly discussed and requested amongst the game development community.