This jam is for making games about apocalypses.
An apocalypse can be an event of destruction on a large scale, such as a war or a disaster, or even a personal apocalypse, such as loss or nearing the end of one's life. The interpretation is up to you, really!
Any game engine can be used, the only rule is that your game is themed around apocalypses in some way, shape or form.
Here are some free game engines you could use:
Twine: For making text adventures/interactive fiction
Ren'Py: For making visual novels
Unity: Can be used for many styles and genres of games (and also walking sims, if you're into that sort of thing)