A list of different resources that should be useful for Steam Deck users.
Add-Ons

• Decky Loader Swiss Army knife group add-ons in your left bar in game mode with customizable applications for easy access, system changes, and game tweaks.
  • Site: https://github.com/SteamDeckHomebrew/decky-loader
  • Install Guide Video: https://youtu.be/eiINSEvGs_8
• Heroic Launcher Add your games from other market places.
  • Site: https://heroicgameslauncher.com/
  • Install Guide Video: https://youtu.be/j8YdKoC6-nE
• CryoUtilities 2.0 performance boost for gaming and memory on Steam Deck.
  • Site: https://github.com/CryoByte33/steam-deck-utilities
  • Install Guide Video: https://youtu.be/C9EjXYZUqUs
• EmuDeck one-stop shop for installing emulators on Steam Deck.
  • Site: https://www.emudeck.com/
  • Install Guide Video: https://youtu.be/Y5r2WZAImuY
• Proton GE change proton versions for specific games for compatibility issues.
  • Site / Guide: https://www.rockpapershotgun.com/how-to-install-proton-ge-on-the-steam-deck (NOTE: Link is a little old but as it is installed through the application store should work all the same.)

Sites

• https://www.protondb.com/ check configurations and Proton GE versions to get your games to work.

I hope this has helped someone in the community. If anyone has any more suggestions of tools or useful sites to add please add them below.
Hopefully we can get this community going!

EDIT: This is intended to be a living post. I will try to update when I can.