Please post links to any free resources you know of and if possible credit the creators. I (and any moderator that can spare some time) will add them to the master list in this very post.
Special thanks to all the resource creators and the people who have submitted the links.

There have been some great submissions since I last updated this master post, this link will take you to the last one I added, so it's worth foraging for anything past the link.



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).


*Disclaimer - I have not had the time to test all of the links, assets and software, therefore I will not be held accountable for any damage these may cause to your computer, zen, ch'i, karma or well being