Here some resources and tools that you can use!

Game Engines
Unity | Godot | Unreal Engine

IDE and Editors
Atom | Visual Studio Community Edition |Visual Studio Code

Pixel Editor
PiskelApp | PyxelEdit | Aseprite (Paid)

Modeling
Blender | SketchUp

Voxel Editors
goxel | MagicaVoxel | Sproxel

Vector/Image Editor
GIMP | Paint.NET | Ormr | Affinity Designer (Paid)

Music/SFX creation/generation: 
Bosca Ceoil | BFXR | Chiptone | Audacity

Tilesets Creation/ Level editor 
Tilesetter |  LDtk

Story Idea Generator:
Seventh Sanctum |  Steampunk Random Story Generator

Management 
Trello | Milanote | ClickUp

---

Colours
Color Hex | Pallet List - Lospec | Flat UI Colors | Adobe Color

SoundBible.com | Freesound | Game Sounds | Youtube Audio Library | Zapsplat 

Assets
OpenGameArt.org | Kenney | Assets - itch.io

3D Models: 
TurboSquid | Poly

Textures: 
Texture Haven | Textures

Fonts: 
DaFont |  Google fonts | Font Squirrel 

Icons
IconArchive | Icons8 | Endless Icons | Game-icons.net

Inspirations
Dribbble | Behance | Interface In Game