What are some alternatives?
When comparing Shovel Knight and SuperTux, you can also consider the following products
Dead Cells - Castlevania-inspired, action platformer with roguelike elements.
Hollow Knight - Descend into the Dark Venture down into a beautiful, ruined world of insects and heroes
Super Meat Boy - Let's start with what's the same: Dr. Fetus is still a jerk, gameplay is super challenging but fair, there are tight controls and great levels and you will die. a lot.
Mega Man Revolution - A fan-made 8-bit-style Megaman side scrolling shooter game.
Secret Maryo Chronicles - Secret Maryo Chronicles is an Open Source two-dimensional platform game and is using an Open Graphics Library for the best possible graphic design and stock performance.
Braid - Resource planning & scheduling for professional services