Unity 3 is a game development tool that has been designed to create amazing 3D environment games.

Scripting languages
Unity supports three scripting languages: JavaScript, C#, and a dialect of Python named Boo. All three are equally fast and can interoperate. All three can make use of .NET libraries which support databases, regular expressions, XML, networking and so on.

Performance
Scripting is frequently thought of as limiting and slow. But in Unity the blazing fast iteration times and ease of use of scripting languages are paired with compilation to native code and thus run nearly as fast as C++. And Unity's JavaScript implementation runs the same speed as C# and Boo.

Visual Properties
Public variables defined by scripts are shown in the Unity Editor. You simple drag objects to set variable references, pick from drop-down lists, and change colors with a color picker. In short, no need to write glue code.
.NET based

Game logic runs on the Open Source .NET platform, Mono. This gives you the full strength, speed and flexibility of one of the world's leading programming environments.

Event System
Simply implement a function and Unity handles all hookup automatically. When you want to add your own events, simply use SendMessage to call any method on any script.

Flexible and Easy
Moving, rotating, and scaling objects just takes a single line of code. Duplicating, removing, and changing properties likewise. Everything can be referenced directly, by name or hierarchy, tags, proximity, or touch.

Simple Co-Routines
Logic flows that involve waiting a bit of time are performed in three lines of code. This makes co-routines easy and robust.

Development
Unity 3 features full MonoDevelop integration in all licenses. This means you get a state-of-the-art IDE that works completely with Unity.

Coding
Unity can automatically sync with MonoDevelop and Visual Studio. All external references are set up so you get full auto-completion on the built-in API.

Debugging
In Unity 3 we added debugger integration. You can pause your game, do single step line by line, set breakpoints, and inspect values. The days of print-based debugging are gone for good.

Profiling
When it comes down to optimizing your game, nothing beats a solid profiler. Again, Unity Pro delivers. Simply bring up the buit-in profiler and you get per-frame stats on where you're spending time and why. When you've found a performance spike, you can drill down and see what exactly was the cause.