Colour pallets:

Color Hex: https://www.color-hex.com/

Pallet List - Lospec: https://lospec.com/palette-list

Audio:

SoundBible.com: http://soundbible.com/

freesound: https://freesound.org/

Youtube Audio Library: https://www.youtube.com/audiolibrary/music?nv=1 

Music creation/generation: 

Bosca Ceoil: https://boscaceoil.net/ 

BFXR: https://bfxr.net/ 

Chiptone: http://sfbgames.com/chiptone

Assets:

OpenGameArt.org: https://opengameart.org/

Kenney: https://kenney.nl/assets

Assets - itch.io: https://itch.io/game-assets

3D Models:

TurboSquid: https://www.turbosquid.com/

Poly: https://poly.google.com/

Textures:

Texture Haven: https://texturehaven.com/

Fonts:

DaFont: https://www.dafont.com/

Google fonts: https://fonts.google.com/

Font Squirrel: https://www.fontsquirrel.com/

Images:

Pixabay: https://pixabay.com/

Unsplash: https://unsplash.com/

Story Generator:

Seventh Sanctum: https://www.seventhsanctum.com/generate.php?Genname=storygen

Steampunk Random Story Generator: https://www.magatsu.net/generators/steampunk/index.php

Management:

Trello: https://trello.com/

Milanote: https://app.milanote.com/