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 list in 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 post, linkwill 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…com/ - Free substances!!
TextureGenerator-Online - Generate textures in browser
http://www.mapzoneeditor.com/ - Free texturing tool from (makers of substance) Dead link 
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
TreeIt | Tree Generator - Foliage generator
Download L3DT Standard Edition - Terrain generator
IKinema WebAnimate - Free web based animation for your 3d characters. No longer free??
Houdini Apprentice | SideFX - 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 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 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
Studio One | PreSonus Shop - Free DAW
http://yamamavcs5.weebly.com/ - VST compatible or standalone synthesizer
https://lmms.io/ - Free open source DAW
Other
[FREE] Launchpad - A free, open-source UE4-compatible game launcher - Programming & Scripting - Epic Developer Community Forums - Open source launcher
Blackmagic Design releases Fusion 7 for free | CG Channel - Compositing package
https://obsproject.com/ - Live streaming and recording
Visual Studio 2022 Community Edition – Download Latest Free Version - 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:
GitHub - Hevedy/PurpleprintKit: Purpleprint 2 - Kit
Free content | Unreal Engine 4 blog
[FREE] grass meshes - World Creation - Epic Developer Community Forums
http://redpolygon.com/free-textures/
[FREE] Foliage Starter Kit - World Creation - Epic Developer Community Forums - fighter5347’s incredible gift
[FREE] Various models - World Creation - Epic Developer Community Forums - Thanks to DaveFace!!
Materials and Textures:
The Monolith - Community & Industry Discussion - Epic Developer Community Forums
[FREE] NEW Textures materials - Asset Creation - Epic Developer Community Forums
Textures only:
http://www.environment-textures.com/
http://cgtextures.com/
http://opengameart.org/textures/all
Blueprints/UMG/BT & Project templates:
[FREE ASSET] Dynamic UMG crosshair - Programming & Scripting - Epic Developer Community Forums - Dynamic Crosshair (thanks to Osman)
[ Free ] Networked UMG Menu w/ Host/Join, Settings, Health/Item replication. All BP! - Multiplayer & Networking - Epic Developer Community Forums - Networked UMG menu (thanks to SaxonRah)
Free Inventory System - Backend - Blueprint - Epic Developer Community Forums - Inventory (thanks to ruohki)
[Community Project] WIP Weather & Water Shader - Game Development - Epic Developer Community Forums - Weather & Ocean (thanks to + friends)
[UPDATED 5/16] A.I. Templates - Bot, Car, & +Flying AI - Programming & Scripting - Epic Developer Community Forums - AI templates (thanks to Peter L. Newton)
UMG and Online Subsystem Blueprint Example - Game Development - Epic Developer Community Forums - SaxonRah’s UMG online subsystem
Learning Templates [Blueprint Power] - Programming & Scripting - Epic Developer Community Forums - Courtesy of Mhousse1247
https://forums.unrealengine.com/showthread.php?59262-AI-Project-Sample-(Blueprint-Only) - Courtesy of Mhousse1247
[FREE] Procedural Rope Bridge - Community & Industry Discussion - Epic Developer Community Forums - procedural physics enabled rope bridge
2D Sprite Sheets & Background Textures:
Glitch | Public Domain Art & Code
Free Stuff
David Hellman .net - Braid
Audio:
https://www.freesound.org/
www.freesfx.co.uk/
www.grsites.com/sounds/
99Sounds - A ton of high quality sound fx collections.
[FREE] Audio Pack - Audio - Epic Developer Community Forums
Tutorials/Books
- 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, , ch’i, karma or well being