You want 3D or 2D? 3D I amke with Unity, 2D is better with Browser-IDE like AGK or Monkey X or processing+javascript,
For the first we can make this jam --> One Game a Month #49 - itch.io
This Jam I often participated in the last years, we have enough time, no restrictions and limitations (the theme there is only optional)
Sorry, I haven't found a good rpg- or fantasy- or adventure-jam