Feel free to post links to useful gamedev tools (of any sort), and I'll add them to a running list.
Coding:
All-in-One Libraries:
Raylib
SDL
SFML
Ready-Made Engines:
Godot
Unity
Testing/Debugging:
Valgrind
Renderdoc - Graphics debugging
Godbolt - Interactive compilation explorer
Memory/Thread sanitizes from Google
LibFuzzer
LibAFL - Another fuzzer
Cppcheck - Static C/CPP analyzer
CToy - Interactive C prototyping environment
Prototyping:
Processing
Audio Creation:
SFXR - FM synthesis sound generator
BFXR - Upgraded version of SFXR
Audio Editing:
FamiStudio - NES-style music tracker
Audacity - Free audio recorder and editor
MilkyTracker
LMMS
Audio Resources:
SONNISS - Royalty-free Sound Effects Collections
Texture Creation:
Texture Editing:
Aseprite
Grafx2
Moai
Pro Motion
Graphics Gale
Krita
Mesh Editing:
Blender
Blockbench
Shaders:
Kodelife - Realtime shader editing (offline)
Shadertoy - Realtime shader editing (online only)
Screen Capture/Recording:
Streamlabs - Streaming and screen capture. Based off OBS
OBS - Open Broadcaster Software
Licecap - Capture screen/desktop to GIF
Editors / IDEs:
Helix (Editor)
Sublime
Code::Blocks
Libraries:
STB
sokol
Large single-header library list
JSON Parser
Misc:
git bisect - Let git show you where you introduced an error