What are some alternatives?
When comparing Hollow Knight and SuperTux, you can also consider the following products
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.
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
Cave Story - Cave Story Tribute Site is a tribute fansite to a Japanese game called Doukutsu Monogatari and translated under the title Cave Story.
Limbo - “Dark, disturbing, yet eerily beautiful, Limbo is a world that deserves to be explored.” Joystiq. “Limbo is as close to perfect at what it does as a game can get.” Destructoid. Buy LIMBO: Special Edition.
Minilens - Libre puzzle platformer for gravity-oblivious aliens