From:http://www.gamedev.net/community/forums/topic.asp?topic_id=324643
Graphics Engines
Ogre 3D
Nebula Device
Jad (formerly Haddd)
Irrlicht
Haaf's Game Engine (hardware accelerated 2D games engine)
Axiom 3D (OGRE for .NET)
TrueVision
Revolution3D
Genesis3D
Crystal Space 3D
Panda3D
Quake 3 Source Code
Quake 2 Source Code
Quake 2 (complete sources)
Tenebrae (Quake with per pixel lights and shaders)
Wild Magic (David Eberly's engine)
Apocalyx
ClanLib Game SDK
DevLib
kjAPI
Portable Game Library (PLIB)
RealmForge GDK
Delta3D
G3D
NeoEngine
QuakeForge
XEngine
Yake
Kyra Sprite Engine
Libraries
Free Game Development Libraries (external list)
Graphics:
Crazy Eddie's GUI system
Cal3D (character animation library)
GLFW (OpenGL Framework)
GLee (OpenGL easy extension library)
DevIL
Game Texture Loader
SDL
Cpw (another OGL framework)
Allegro
Open Scene Graph
Corona
Titan
SFont
CxImage
CImg
FreeImage
BMF_Font
BFont
FreeType (font rendering library)
PaintLib
GLEW (OpenGL extension wrangler library)
gluX
GLUT
FreeGLUT
Open Inventor
FTGL (OpenGL Font Library
nVidia Scene Graph SDK
OpenSG
ParaGUI
LibUFO (OpenGL GUI Toolkit)
GPUmesh
GNU Triangulated Surface Library
libASE
lib3DS
GLOD (Geometric Level of Detail for OpenGL)
Video:
FFmpeg
Dirac
Theora
XviD
Networking:
RakNet
OpenTNL (Torque network library)
HawkNL
OpenPlay
ReplicaNet
Game Networking Engine
Sound:
FMOD
OpenAL
Audiere
BASS
libsndfile
Ogg Vorbis
Physics and Collision:
Open Dynamics Engine (ODE)
Tokamak
Newton Game Dynamics
NovodeX SDK
Physical
True Axis
Open Dynamics Framework
ColDet (Free 3D Collision Detection Library)
Opcode
RAPID
FreeSOLID
V-Collide
Scripting and XML:
Python
IronPython
Lua
AngelScript
CInt
EOS
GameMonkey Script
Guile
IO
javascript
Squirrel
Small
Ruby
Tcl
Perl
LibXML
TinyXML
Expat
Apache XML libraries
ezXML
Compression and File Systems:
zlib
bzip2
LZMA SDK
LZO
PhysicsFS
#ZipLib (native C# archive library)
SharpFS (native C# VFS)
unrarlib
ZipArchive
Note: Much of the above lists (but not all) were taken from this page , maintained by Kylotan here .
Applications and Utilities:
Development Environments:
Visual Studio 2005 Express
Code::Blocks IDE
Dev-C++
SharpDevelop
ActivePython
Graphics Development:
gDEBugger
FX Composer
RenderMonkey
NVIDIA SDK
ATI Radeon SDK
DirectX Developer Center
NVIDIA Cg
Sh (shader language)
Modeling:
SoftImage|XSI Mod Tool
Milkshape 3D (not free, $25)
Wings 3D
Blender
Anim8or
DeleD
World Building:
Quake Army Knife (QuArK)
GtkRadiant
Getic3D
Audio:
ModPlug
Audacity
SynthEdit
Buzz Machines
KVR Audio (not actually software, but has tons of links)
Images:
Paint.NET (excellent free image editor)
The GIMP
BMFont (font texture generator)
Media
Textures:
Transmogrifying Textures Vol. I (NVIDIA)
Mayang's Free Textures
3D Cafe's Free Textures
Absolute Background Textures Archive
Image * After
Media Link's Free Backgrounds and Textures
Free Game Textures
Seamless Textures -- Absolute Cross
3D Millenium Free Textures
Pixel Poke
The Texture Studio
Textures
Marlin Studios
Free Foto
Free Textures
Free Textures
MorgueFile
Psionic3D
Models:
3D Millenium Free Models
Polycount
Marlin Studios
Free 3D Model Collections
Free 3D Models
Digital Animators Models
Psionic3D
Free 3D Models for 3D Studio Max
Sprites
This thread has lots...and lots...and lots...
Sounds:
SFX and Music Resources (another long GDNet post)
Jamendo (Creative Commons licensed music)
A1 Free Sound Effects
Sound Effects
Tintagel's Free Sound File Archive
Free Sound Effects
Sound Hunter
Wav Sound Complete Archive
deusX Sound Design
FindSounds (sound search engine)
Absolute Sound Effects Archive
That's all I've got for now. Still need plenty of resources in the art and music department...free sounds, free textures, free models, free music, and of course, many more utilities.