Many many programmers outsource game library frameworks to build game like for example if u want to build a game like candy crush berry match 3 engine is available to guide you through the path with unity3d. In game there are many sites you can download paid and free asset. scirra, www.gamedevmarket.net,
www.assetstore.unity3d.com ,www.gameart2d.com
for those that are not too good with graphics and 3d design. look for how to create the game sound using any tool. If u already have your own design no need of downloaded any.
The audio is from voice recording in 2d game you can download games audio software.

For the coding aspect there are many tutorials on udemy and YouTube on game development try to practice and explore all possibilities. learn how to use game libraries , framework and engine. it is possible to create an HTML5 game without any engine with HTML5 canva ,css and Javascript. You might copy some codes and customize it to display the desire result. Cordova/phonegap/intel xdk can build HTML5 games. learn how the events, method interact.


Android studio or eclipse can be use to create games for Android with Java or c++ where NDK is required with libgdx.

If you noticed many game are following the same trends because they paid to acquire the repo . The code is refurbished and more features are added to make it unique.



Gamesalad and game builder are drag and drop tool for creating games without any programming knowledge or experience .

Game source

http://www.java2s.com/Open-Source/Javascript_Free_Code/Game/List_of_Free_code_Game.htm

http://osgameclones.com

https://github.com/leereilly/games

http://gamecodeschool.com/unity/simple-patrol-chase-ai-tutorial-with-unity-2d/


Java games

http://www.java2s.com/Open-Source/Java_Free_Code/Game_shooter/Download_Space_shooter_Free_Java_Code.htm


course guide

https://www.udemy.com/courses/development/game-development/

YouTube
Lynda

SOME GAME DEVELOPMENT SOFTWARE




Unity
3d

Unreal Engine

Stencyl

CryENGINE


3ds Max


Blender

Construct

Marmoset

Toolbag

Massive

Maya


MODO

Mudbox

Oculus

Photoshop

Softimage

DesignerSubstance


Painter

TopoGun

UDP
game server

ZBrush