This is _The Best List_ for (mostly) free resources:

https://github.com/everestpipkin/tools-list

Some MVPs from that list:

• GB Studio - A drag and drop gameboy interface that lets you do some scripting. Export to html or an actual gameboy rom!
• PuzzleScript - An open source, HTML5 puzzle-game oriented editor.
  
• Twine - An open-source tool for telling interactive, nonlinear stories. Has a big community and multiple versions and themes.
  
• Ren'Py - Free, open source cross-platform Visual Novel development engine.
  
• Godot - Perhaps the most complete and well documented open source engine, for 2d and 3d.
  
• Adventure Game Studio - Free engine for making point & click adventure games.  Good forums and strong community around this one.
  
• Visual Pinball - A pinball making engine.  Yo, pinball is legit.
  
• If you're using Unity, check out the list of extenders that will save you time and energy.

And all the Art/Sound stuff is great.

Scope

Remember to think tiny and make a 'complete' experience.  Doesn't have to be an infinite dungeon crawler or a multiplayer hero shooter.  (old) Arcade games are a great inspirational point for simple concepts.

Common Roles that are helpful on a team (you don't need all of these):

-Programmer - Doesn't matter what language.

-Writer - esp for narrative games that use things like Twine or Ren'Py. 

-Musician - For music and/or sfx.  You can also find royalty free music most places.

-Artist - 2D, 3D, User Interface (buttons, frames, etc).  An artist will make your nonsensical house of cards look like the Palace of Versailles.

-Project Manager - It takes a lot of work to keep everyone on task using a tool like Trello, Kanban, Codecks, etc.  PMs also usually unblock problems for other team members (ex. I don't know what art program to use because I'm broke - PM find a good easy to use solution).

Theme / Mechanical Twist:

The theme is "Pop!"

The mechanical twist is "Game Over in 60 Seconds" The main playing of your game should not exceed one minute.

Please do not let this stop you from making a game.  The theme is supposed to be a fun guide to get your brain doing backflips.

An example theme is "Waves".  You could make a game with waves of enemies, or a game about surfing, or a game about communication via radio waves, etc etc etc.

An example of a Mechanical Twist is "One button".  Your game must be playable by pressing only one button.  Hilarious, right?