LevelSmith: Foundry 2D

Foundry2D is an open source 2D platformer prototyping tool focused on rapid iteration, maximum customization, and ease of use. Use eight unique tiles, four different enemies, coins, and checkpoints to construct playable 2D platformer levels.

Then, modify everything!

Easily change player movement, enemy behaviors, camera settings, and every single asset! All textures, animations, and audio can be replaced with a press of a button. Share your levels with others, bringing all your customization with it.