UltraTux

THE STORY
The Evil Crocodile Nolok is causing havoc in Antarctica, grabbing penguins and locking them in cages for unknown crocodilian reasons. It's up to everyone's favourite Linux mascot to try and save them!

...yes, this is obviously heavily inspired by SuperTux. Maybe play that as well.
Also is similarly open source.

THE CONTROLS

• WASD / Arrow Keys - Move
• Space - Jump
• Left Shift - Run
• Escape - Exit Level

Also has at least some controller support
(evidence: is playable using my controller)

THE EDITOR

I have tactically eschewed paragraphs of text explaining how the editor works in favour of actually releasing this project. Basically, you're on your own here. Good luck!
If you do figure out how to use the editor, high quality levels will be considered for inclusion into the Bonus Islands.