Here's where jam participants can discuss game engines and development tools. Below is a brief list of free ones that are worth looking into, some introductory resources to check out, and a list of well known games made with each in order to get an idea what the tools are capable of.

• Unity: The most popular game development tool, which is capable of creating both 2D and 3D games. Some C# scripting will likely be required, but a lot can be accomplished in the level editor alone, and with the help of the asset store.
Notable Games: Gone Home, Hearthstone, Cities Skylines, Ori and the Blind Forest, Cuphead
Resources: Unity Beginner Documentation; Sebastian Lague Intro Playlist; A little pricey, but this kit available on the asset store is well worth the cost if you're interested in making first-person exploration games.

• GameMaker: A relatively beginner friendly tool specializing in 2D games. GameMaker features a drag and drop interface but can also be programmed entirely with it's own unique scripting language.
Notable Games: Spelunky, Hotline Miami, Hyper Light Drifter, Undertale
Resources: Making A Game With No Experience; Shaun Spalding Tutorials;

• Twine: A tool used to create interactive narrative and text based games. While it can be used with no coding, CSS and JavaScript can be integrated for additional functionality.
Notable Games: Depression Quest
Resources: Twine Wiki; (Twine is really easy to pick up and shouldn't require much reading to get started)

• Unreal Engine: Noted for its visual quality, and used in AAA and indie games alike, especially for first person shooters. While a lot of effort has been put into making the engine more accessible, it will still require some research and knowledge of C++.
Notable Games: Bioshock, Unreal Tournament, Mass Effect Trilogy, Life is Strange, Rocket League, Fortnite
Resources: Unreal Engine Official Documentation; First Person Exploration Kit similar to the Unity asset listed above.

• RPG Maker: While very focused on JRPG style games, RPG Maker is also pretty straight-forward and easy to use. It requires no coding, but additional functionality can be added with custom scripts using the Ruby language. There are multiple versions, each with a free trial, but RPG Maker VX Ace Lite is a completely free version, which should serve the needs of this jam.
Notable Games: To the Moon, Lisa
Resources: RPG Maker VX Official Documentation;

• Superpowers: I'm not very familiar with this engine myself, but it was recommended by Potatoes Are Not Explosive in a previous jam. It's a collaborative HTML5 engine that actually runs in the browser. If you set up hosting for it you can get google-docs style collaboration, which is not great for proper software engineering but it's awesome for game jams!
Resources: http://superpowers-html5.com

• Puzzlescript: An HTML5 based game engine designed for puzzle games. Recommended by Nina for those who don't want to get into too much coding.
Resources: https://www.puzzlescript.net/

• Bitsy: Also recommended by Nina, Bitsy is a grid based, retro-style engine that's works well for top-down adventure games.
Resources: http://ledoux.io/bitsy/editor.html

Just going to chime in here with a recommendation of GDevelop. It's an open source 2D engine that feels like mixture of Stencyl and Construct 3. It requires no programming languages, although it can be extended using Javascript, if you want.  Games can either be compiled or output into HTML5 that can be uploaded to places like Itch.io to run in browsers.

I've found it exceptionally well suited to: Point-and-click adventure games, platformers, puzzle games, and 2D scrolling shooters. I'm sure you can easily make other genres as well, but I'm new to it.

You can find more details here:

GDevelop site

Tutorials and Wiki

Examples

If you want to see my own test I made after poking around in it for about 13 hours, you can see that here.