RenderDoc is a stand-alone graphics debugging tool.
CRYENGINE is a powerful real-time game development platform created by Crytek.
Modifications to third party software used by UE4
Amazon Lumberyard is a free AAA game engine deeply integrated with AWS and Twitch – with full source.
mimalloc is a compact general purpose allocator with excellent performance.
The original sources of MS-DOS 1.25 and 2.0, for reference purposes
In short, Forge Networking is a free and open source multiplayer game (multi-user) networking system that has a very good integration with the Unity game engine. You wanna make a multiplayer game or real time multi-user application? This is the library for you.