Free Software:
Game Engines
https://www.unrealengine.com/ - The one & only!!!
Texturing & Image Tools:
https://share.allegorithmic.com/ - Free substances!!
http://cpetry.github.io/TextureGenerator-Online/ - Generate textures in browser
http://www.mapzoneeditor.com/ - Free texturing tool from Allegorithmic (makers of substance) Dead link
http://cpetry.github.io/NormalMap-Online/ - Generate normals in browser
http://www.krita.org/ - Image Editor/Painting program
www.gimp.org/ - Image Editor/Painting program
Irfanview - Open, convert, optimize, and use batch processing (renaming for example) for nearly any image type.
SpaceScape - Create an outer space skybox with stars & nebula's.
xNormal - Bakes out normal/AO/height and many other maps from a high poly mesh.
handplane - Tangent space calculator for converting Object space normal maps.
RoadKill UV Tool - Unwraps your models from 3dsMax/Maya/Softimage.
Wood Workshop - Wood texture generator (credit to 94)
Modelling, Sculpting, Animation and Mesh Optimization Tools:
http://pixologic.com/sculptris/ - Free sculpting + painting tool from the makers of ZBrush
http://www.blender.org/ - Free modelling/rigging/scuplting/animating tool
https://www.simplygon.com/games - LOD generator and mesh optimization (cloud based, free for personal use)
MakeHuman - Free 3D Humanoid character creator (Open Source).
3dsMax Rock Generator - MaxScript for quickly creating high quality rock meshes.
Autodesk FBX Converter - Quickly convert OBJ/DXF/DAE/3DS files to an FBX format file.
TerreSculptor - Currently in beta, is very similar to World Machine.
http://meshlab.sourceforge.net/ - modelling app
http://www.evolved-software.com/treeit/treeit - Foliage generator
http://www.bundysoft.com/L3DT/downloads/standard.php - Terrain generator
IKinema WebAnimate - Free web based animation for your 3d characters. No longer free??
http://www.sidefx.com/index.php?opti...245&Itemid=400 - Free Apprentice edition of Houdini (watermarked and of limited use but good for learning)
http://www.fragmosoft.com/ - 'Fragmotion can be used without buying it (for 50 USD), if you type in the prayer text appearing weekly'
http://www.123dapp.com/meshmixer - A mesh mashup tool from Autodesk, some pretty cool sculpting tools too
http://www.wings3d.com/ - I just found this yesterday, now my all time favorite 3D modelling program - it's the only one I am capable of making anything with :/
http://www.mit.edu/ibaran/autorig/pinocchio.html - Auto rig meshes (with source code), would be good if this could be turned into a simple UE4 plug-in (hint hint)
Audio and Sound Tools:
http://audacity.sourceforge.net/ - Audacity, a free audio editor
http://www.bfxr.net/ - an awesome online sound effect generator
https://shop.presonus.com/products/s...tudio-One-Free - Free DAW
http://yamamavcs5.weebly.com/ - VST compatible or standalone synthesizer
https://lmms.io/ - Free open source DAW
Other
https://forums.unrealengine.com/show...-game-launcher - Open source launcher
http://www.cgchannel.com/2014/11/bla...on-7-for-free/ - Compositing package
https://obsproject.com/ - Live streaming and recording
http://www.visualstudio.com/en-us/pr...munity-vs.aspx - Community edition of Visual Studio (highly recommended!!)
http://blog.bahraniapps.com/gifcam/ - Capture gif's
http://www.mapeditor.org/ - Tiled 2d map editor
Free Assets/Resources:
Models:
http://tf3dm.com/
http://archive3d.net/
http://www.3dmodelfree.com/
http://www.creativecrash.com/3dmodels
http://www.blendswap.com/
http://www.sharecg.com/
http://www.yobi3d.com/#!/
Animations & Motion captures:
http://www.turbosquid.com/search/motion-capture/free/
http://mocap.cs.cmu.edu/
http://animation.comp.nus.edu.sg/nusmocap.html
http://birhandursun.com/motion.php
http://www.3d-brothers.com/index.php/
http://www.motioncapturedata.com/
Models, Materials & Textures:
https://github.com/Hevedy/PurpleprintKit
http://www.michalorzelek.com/blog/?cat=9
https://forums.unrealengine.com/show...e-grass-meshes
http://redpolygon.com/free-textures/
https://forums.unrealengine.com/show...401#post227401 - fighter5347's incredible gift
https://forums.unrealengine.com/show...Various-models - Thanks to DaveFace!!
Materials and Textures:
https://forums.unrealengine.com/show...8-The-Monolith
https://forums.unrealengine.com/show...ures-materials
Textures only:
http://www.environment-textures.com/
http://cgtextures.com/
http://opengameart.org/textures/all
Blueprints/UMG/BT & Project templates:
https://forums.unrealengine.com/show...-UMG-crosshair - Dynamic Crosshair (thanks to Osman)
https://forums.unrealengine.com/show...cation-All-BP- - Networked UMG menu (thanks to SaxonRah)
https://forums.unrealengine.com/show...System-Backend - Inventory (thanks to ruohki)
https://forums.unrealengine.com/show...ommunity+ocean - Weather & Ocean (thanks to DotCam + friends)
https://forums.unrealengine.com/show...-amp-Flying-AI - AI templates (thanks to Peter L. Newton)
https://forums.unrealengine.com/show...eprint-Example - SaxonRah's UMG online subsystem
https://forums.unrealengine.com/show...lueprint-Power - Courtesy of Mhousse1247
https://forums.unrealengine.com/show...eprint-Only%29 - Courtesy of Mhousse1247
https://forums.unrealengine.com/show...al-Rope-Bridge - procedural physics enabled rope bridge
2D Sprite Sheets & Background Textures:
http://www.glitchthegame.com/public-domain-game-art/
http://www.dumbmanex.com/bynd_freestuff.html
http://www.davidhellman.net/braidbrief.htm
Audio:
https://www.freesound.org/
www.freesfx.co.uk/
www.grsites.com/sounds/
99Sounds - A ton of high quality sound fx collections.
https://forums.unrealengine.com/show...REE-Audio-Pack
Tutorials/Books
http://www.kitatus.co.uk/ - Some great tutorials and example projects to get you started in UE4
Other
IES Lighting Profile Archive - A great resource for IES photometric lighting textures (Lithonia Lighting).
