I have two formats I want to work with, and two jams, so that lines up perfectly. I’ll decide which one I want to do for which when this MiniLD starts.

2 or 2.5D:
Artwork and tilesets: GIMP
Level design: Tiled Map Editor [Thanks for bringing this to my attention! If I’d had this last LD, I probably could have made a game instead of making a failed JSON parser to initialize my levels!]
Engine: GameMaker: Studio – Standard [and Tiled2GM to bridge the gap]

3D:
Models: Blender and default cubes
Textures, excessive “billboards”, and GUI artwork: GIMP
Engine: Unity 5