Here's the Free Full Version of Unity for Windows with Unity Pro and Android trials.

Unity is a multiplatform game development tool, designed from the start to ease creation. A fully integrated professional application, Unity just happens to contain the most powerful engine this side of a million dollars.


Unity 3.5 gives more power to artists and developers to minutely control complex elements while still preserving our famous ease of use and access. Whether you are an indie dude with a dream or a major studio mapping out your next big hit, Unity 3.5 makes the road to your awesome game shorter, faster, and a lot more fun!

System Requirements

System Requirements for Unity Authoring

Windows: XP SP2 or later; Mac OS X: Intel CPU & "Leopard" 10.5 or later. Note that Unity was not tested on server versions of Windows and OS X.
Graphics card with 64 MB of VRAM and pixel shaders or 4 texture units. Any card made in this millennium should work.
Using Occlusion Culling requires GPU with Occlusion Query support (some Intel GPUs do not support that).
The rest only depends on the complexity of your projects!.

System Requirements for Unity iOS Authoring

An Intel-based Mac
Mac OS X "Snow Leopard" 10.6 or later
The rest only depends on the complexity of your projects!

System Requirements for Unity Android Authoring

In addition to the general system requirements for Unity Authoring
Windows XP SP2 or later; Mac OS 10.5.8 or later
Android SDK and Java Development Kit (JDK)

System Requirements for Unity-Authored Content

Windows XP or later; Mac OS X 10.5 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.
Android authored content requires devices equipped with:
Android OS 2.0 or later
Device powered by an ARMv7 (Cortex family) CPU
GPU support for OpenGLES 2.0 is recommended


Unity 3.5.3

This release of Unity primarily contains fixes to Unity 3.5. For more information about recent features, see the Unity 3.5 Release Notes.

Shuriken Particle System
Built-in Pathfinding
Upgraded Occlusion Culling & new LOD
Google Chrome Native Client deployment
Linear Space Lighting and HDR

Improvements

Audio: Fixed audio distortion when using gapless MP3 encoding.
Cache Server: Fixed connection issues.
Development players will now show file names and line numbers in stack traces again.
Graphics: Added Optimize Mesh Data option to Player Settings. Turning it on will remove unused mesh components (e.g. will remove all tangent vectors if none of your shaders use normal mapping). Use this both for game size and runtime performance.
Graphics: Added Camera.transparencySortMode to control how transparent objects are sorted. If you use a perspective camera for a 2D game, you can have proper object sorting now!
Graphics: Mesh.Clear now will keep the existing vertex layout; this is more efficient if you are recreating meshes at runtime. If you want to completely clear the mesh, including vertex format layout, use mesh.Clear(false).
iOS: now automatic inclusion of native plugins will also respect "Symlink Unity libraries" flag. Turn this flag off when making archive builds.
Native Client: Fixed crashes in script code in 64-bit NaCl (64-bit Windows or Linux).
Profiler: Reduced memory footprint of profiler when viewing large frames (deep profile)
Web Player: Make browser more responsive to user input on Windows.

Known Issues

Android: Auto-rotation doesn't work on Kindle when 32bit Display Buffer is selected. Please force orientation in PlayerSettings.

Fixes

Unity for Native Client has been updated to a new version of the NaCl SDK, which fixes some problems. Shipping NaCl games need to be rebuilt with Unity 3.5.3, as they will no longer work in future versions of Google Chrome otherwise!

Android: JDK 7 installations are now automatically detected on windows.
Android: Reading player preferences using the wrong value type now return the default value.
Android: Fixed a rare race-condition when quitting the application.
Android: Added support for gdbserver being packaged inside the application.
Android: Use of spaces in keystore alias/password is now allowed.
Android: Added better failure message when the wrong key password is provided.
Android: Force SHA1 digest algorithm when signing the application, to make sure it's accepted by Google Play Store.
Android: Force RSA key algorithm when creating keys, as suggested by Google.
Android: Workaround for the bug with Kindle's compositor where it incorrectly uses the alpha values from the Display Buffer.
Android: Added warning for shaders which compilation might cause crash on sgs2 updated to ics.
Android: Fixed returning from pause on Eclair devices
Android: fixed perf regression with batching/dynamic geometry on PowerVR GPUs.
Cache Server: Fixed problem where native assets (prefabs, materials, etc) would not refresh in the Editor when updated on disk and cache server is active.
Editor: Rotation doesn't create leftover animation curves anymore
Editor: Fixed "Deprecated EditorExtensionImpl" assets show up in projects converted from Unity 3.4
Editor: Fixed crash when selecting multiple ScriptableAssets of different types.
Editor: Fixed up serialized property error that causes a null ref when an array is the last element being drawn.
Editor: Fixed up asset labels so that they get saved to meta data and displayed in the inspector properly.
Editor: Correctly clear drag and drop buffer so that old data does not stay around causing issues.
Editor: Fixed wrong gizmo rendering on Windows with extremely high quad counts (e.g. drawing 10000 shaded cube gizmos).
Editor: Fixed crash on Windows when you have assets with names like "Tree A" and "TreeA" in the same folder ("revenge of MS-DOS short names!").
Graphics: Fixed static batching when there are source meshes without UV channels.
Graphics: Fixed CombineMeshes() outputting wrong vertex count. This fixes a bug with combined meshes not drawing on some graphics cards.
Graphics: Properly validate array size when setting Mesh.vertices from script.
Input: Correctly detect controller after it has been reconnected on Windows.
Input: Ignore obsolete DirectInput registry settings.
iOS: Fixed automatic .a plugin inclusion into Xcode project.
iOS: Fixed all the issues with splash orientation.
iOS: fixed issue with native UI on top of unity view with non-animated rotation.
iOS: Fixed linking with xcode4.5 dev preview
Mobile: Added additional logging when initializing the profiler (over Wi-Fi or USB), to aid debugging when device is not seen by the editor.
Mobile: Fixed fixed function shader generation in case of more then one TexGen CubeReflect samplers.
NavMesh: Optimize navmesh bake memory-usage. Instead of crashing, returns error when out of memory.
NavMesh: Setting agent destination does not break stopping distance behavior.
NavMesh: Agent respects explicitly set rotation of transform when updateRotation is set.
Networking: Fixed problem with connecting to a password protected server using a GUID.
Shaders: Fixed surface shader decal:blend mode when normal mapping or specular was used.
Shaders: Various fixes to mobile shader translator (HLSL -> GLSL compiler).
Shaders: Fixed incorrect fog on some shader model 3.0 shaders on Windows.

Upgrade guide

In Unity 3.4 realtime lights were not affecting static objects. In Unity 3.5 realtime lights always affect static and dynamic objects.

The result of this is that if you had previously setup your lighting to work around this bug, then you will now get worse performance as you will receive the lighting twice. It will also look different since your lights will be added twice to the scene.

The correct way to use these lights is to use a single auto directional light and remove the realtime only light.

If you wish to have different realtime lighting than static lighting, you should using light culling masks to affect only dynamic objects.
Upgrade Guide