https://itch.io/jam/open-jam-2019
https://opensource.com/article/19/9/open-jam-2019
I have no affiliation or inside knowledge about this, but it looks legit to me. Runs from Sept 27-30 (80 hours).
Guidelines (cut and pasted from the site):
* You can use any tools to create your game and it can run on any platform, open source tools and platforms are encouraged.
* There is a new voting category for "Open Source Karma" based on open source friendly your game is i.e. how many open tools you used, if your game runs on an open platform, and a nice github repo. See table below.
* It is very important to list all the open source tools you used and link to your git repo in your game entry, so you can get credit for your Open Source Karma
* Games source should be available and licensed as open source.
* You can create your own assets or use existing, openly licensed assets (e.g., Creative Commons).
* You can work solo or on a team.
* The theme will be announced at 1:00 PM September 27th (US Eastern).
* Judging will run Sep 30- Oct 8th and will be peer-based.
* Games require a minimum of 10 ratings to place in the top 3
* The top three games will be featured and playable at All Things Open.
* Games must be original for Open Jam, they can't be entries submitted to other game jams or forks of other games. You can use any tools to create your game and it can run on any platform, open source tools and platforms are encouraged.