In no particular order, here are answers to some frequently asked questions. Please let me know if anything's unclear or you have more questions and I'll keep this updated.
> Can we use Unity or Unreal Engine?
> Can we use pre-made assets?
Absolutely, although many people will create their own. I'd recommend adding some attribution in your GitHub repository's README.
> Can we use pre-made code?
The use of game engines, libraries, templates for new games, etc. is fine. In fact, it's highly encouraged! Taking a game you've been working on for months, or forking a game and changing some pixels is probably not in the spirit of the jam :)
> Can we sell the games (for the jam or post jam)?
> Is there a twitter hashtag?
The official hashtag is #GitHubGameOff. We 💜 seeing work-in-progress screenshots throughout the month! <3
> Are games allowed if they contain 18+ content?
No restrictions on content, but if it's something I wouldn't show my kids or grandparents... then it may be less likely that it'll appear on our blog 😎 Please also see itch.io's note on adult content.
> What are the voting categories?
Similar to last year, games will be rated on the following: Overall, Gameplay, Graphics, Audio, Innovation and Theme Interpretation.
> What kinds of licenses are required/accepted for the public GitHub repo?
You're welcome to use whatever kind of license you wish! See this documentation for tips on choosing / applying a license.
> Can I edit the game after the submission period?
Please don't change the game on the itch.io page until after the voting period ends. If there's a bug that seriously affects/prevents playability that's a "quick fix", please feel free to address it. Just leave a note on the itch.io page saying what you changed and why. Since the code is not being judged, you can update the GitHub repository any time.