What software do you need to create a game?

Unity is a good starting point. It is free and there are a lot of pre made assets to build games and or prototypes quickly.
http://unity3d.com/

UDK is a good, free option as well:
https://www.unrealengine.com/products/udk/

If you want to create games with their latest, it will cost you ~$20 a month:
https://www.unrealengine.com/what-is-unreal-engine-4

In addition, the following will be helpful for asset creation:
For modeling, a free option is Blender:
http://www.blender.org/

For image manipulation and a good alternative to Photoshop, Gimp:
http://www.gimp.org/

If you are more interested in the technical side of things and have a game engine that you want to work with, you will need a programming IDE.
Unity comes with a programming IDE called MonoDevelop. It is included with the installation of Unity but here is a link to read about it:
http://monodevelop.com/

If you are on a Mac and want to write in Objective C, C, C++, other languages, you can get a free programming IDE from the OSX app store or here:
https://developer.apple.com/xcode/downloads/

For Windows, Visual Studio:
https://www.dreamspark.com/student/

For Linux and all OS's really, Eclipse:
http://www.eclipse.org/

It is the game engine that run the original Doom, Quake, Wolfenstein etc. and is released for free from ID below. There are XCode project files there as well to easily load into XCode.
https://github.com/id-Software

The original Doom source:
https://github.com/id-Software/DOOM

A fun creative C++ toolkit called OpenFrameworks which is not a game engine per se but you can build games in it for many platforms. Check out the projects created with it on their site:
http://openframeworks.cc/

There are a lot of great free options available to get started on making games.

Game engine:
Construct 2: https://www.scirra.com/construct2
Game Maker: Studio: https://www.yoyogames.com/studio
Unity 3D: http://unity3d.com/

Sound:
SFXer (Make and save sounds) http://www.superflashbros.net/as3sfxr/
Audacity (Record, modify, and mix sounds) http://audacity.sourceforge.net/

Art:
Almost any paint tool will work!
Hexels: (Draw hexagon-based artwork) http://hexraystudios.com/hexels/
Graphics Gale: (2D, animations, sprite sheets) http://www.humanbalance.net/gale/us/

If you don't mind something a bit more specialized, there are some tools/engines that include everything in one spot. My favorite for this is:
Puzzle Script (Art, code, and sound all in one place, only good for making puzzle games) http://www.puzzlescript.net/

Unity and Unreal Engine are very powerful tools but the learning curve is steep. If you want to start making games immediately a more approachable tool may fit your needs:

• GameMaker is a great engine to start writing games with and has been used to release many popular titles (Spelunky, Gunpoint, Dust Force).


• Several tutorials are available to help you get started.

You need 3 main tools - a game engine, tools for art and sound.

You can use either Unity or Unreal if you are looking for a professional engine, they both have a free or very low cost version to get you started. They will enable you to build games on many different platforms and to port your games. If these engines are more complex than you need take a look at Game Salad. One of the things I like most about Unity is their Asset store. You can buy (or get for free) a number of pre-built components, art assets and sounds that you can use in your game.

For art, you can use things like Maya, 3DS Max, Photoshop, Illustrator or you can go the free route and look into the dozens of free painting and drawing packages available. On top of that you can look into royalty free art either from the Unity Asset store or on the web in general.

Finally for sound using something as simple and free as Audacity or Garage Band will take you a long way in creating a sound track. If you really want to get into it you should look at FMOD to enable dynamic sound and ProTools for high end mixing.

There are lots of options you need to find ones that fit your style, skills and goals.

Hey Dasheez

I have some friend creating games using "Unity", with absolutely no knowledge of game development :)
http://unity3d.com/5?gclid=CO-nneGhi8ECFQhbfgodg2EADw

Never used it myself, but it's worth checking up some reviezs and video, and eventually try the licence see if you like it.

;)

It depends on many things.
Web, mobile, standalone etc.
iOS, Android, Windows phone.

The software or IDE (intergrated development environment) is secondary (or even lower down the list) to other things.

A game concept, a target audience for who would like to play the game etc.

The first game I wrote was a quiz, which was more an exercise in creating something my friends would like to play (that was 30+ years ago)
Now there are so many tutorials and free libraries/tools to make the creation of very flashy and impressive looking games that the actual need to be a strong programmer has been reduced and now the big thing is the idea.

However to actual answer the question. Any computer language can be used to create a game, however to create mobile based games tools like Unity, cocos2dx etc are extremely powerful and allow the user to create a game which can then be deployed (played) on many different platforms from web, mobile devices and even consoles.