Bitverse-unity-gui, aka bit-gui, allows developers to visually edit the gui layout, skin and animation using the unity3d editor.

It works on top of the default immediate mode gui from unity3d engine, but it is not immediate mode, it is more like a traditional component based frameworks.

Layout, skin and animation may be packaged in unity3d prefabs, scenes and assetbundles and treated as assets of your game development pipeline.

Current version screenshot:

Here is the current webplayer demo showing almost all GUI system features: http://wiki.bitverse-unity-gui.googlecode.com/hg/demos/editor_demo-current-version.html

A simple calculator demo: http://wiki.bitverse-unity-gui.googlecode.com/hg/demos/bitverse-unity-gui-calulator-demo-2010-02-04.html

All demos source codes are inside the main package download.

You may also want to look the unityforms from Marcelo Roca. It has a WinForms like approach.