Unity 3D - fun and simple

*Fully Integrated Editor
The Unity game engine is happily married to the Unity development environment. This tight integration allows the Editor to do everything a published game can do. The simple, visual, and intuitive nature of the Editor makes building games fun again.
Play, Pause, and Step

Click the Play button to instantly run your game. Pause and Step forward to analyze complex behavior in detail. While the game is running (or paused), you can alter values, assets, or even scripts! This means you can do more experimentation and more testing for a better final game.
Easy Editor Customization

Streamline your workflow using simple, Editor-specific scripts. We wrote the Editor using Unity’s own scripting, so anything we can do in the Editor, you can do as well.
Customizable Editor Layout

Choose from one of many built-in application arrangements, or create and save your own. Different tasks might benefit from different arrangements, so use easy hotkeys to switch arrangements as needed.
Editor Gallery

*Drag 'n Drop Everything

Visually drag assets and objects in the editor to assign Textures, Audio, Behaviors, and script variables. Create logical GameObject hierarchies to manage and maximize your game's functionality.
Prefabs

To streamline the repeated use of complex GameObjects, you can turn one or more of them into a Prefab. This Prefab can then be easily placed throughout the game or instantiated at runtime. Any changes to the original prefab are propagated to all dependents, so both major and minor adjustments can be made very quickly to a large number of GameObjects.



A few Pictures:







*System Requirements:

System Requirements for Unity Authoring
Windows XP SP2 or later; Mac OS X "Tiger" 10.4 or later.
Graphics card with 64 MB of VRAM and pixel shaders or 4 texture units. Any card made in this millennium should work.
The rest only depends on the complexity of your projects!.

System Requirements for Unity iPhone Authoring
An Intel-based Mac
Mac OS X "Leopard" 10.5.4 or later
Using Occlusion Culling requires NVIDIA or ATI graphics card
The rest only depends on the complexity of your projects!

System Requirements for Unity-Authored Content
Windows 2000 or later; Mac OS X "Panther" 10.3.9 or later
Pretty much any 3D graphics card, depending on complexity.
Online games run on all browsers, including IE, Firefox, Safari, and Chrome, among others.

Link Download:
Download the trial version on Unity Homepage:Unity 3D Homepage

I have a problem with unity 3d. Whenever I try to open it, it doesn't work as in it doesn't even show up in Processes. If u can help me that would be great!

@Swishpop:
I've never get this problem, but there are some common fixes that you should try out
Have you ever run Unity 3D Before? (Run it fine, without any problem)
+If so, then maybe you should try restoring your system back to that point and use it (This solution will fix almost every problems though)
Here's the guide to system restore on Windows 7 Microsoft FAQ
+If you've never tried running Unity 3D before and you are using Windows
Well, try the following
+Try running it as Administrator
If not work then:
+Right click on Unity's Icon and choose Properties
+Go to Compability tab and check Run this program in compability mode for and choose Windows XP Service Pack 2 (You can go for 3 though)
+Re-run it
If still not work then you should try Re-installing it
If none of the above solutions work (Which is seriously a technical problem), then you can try to ask the Unity Community, they'll give you your answers (Though it may took some time), you can visit it here: Unity Community FAQ

Best regard ^.^