I have built myself a game engine from the ground up because I couldn't find one that satisfied my needs for my various game projects. I have made a 2D platformer with levels read from png files, a half-finished recreation of Funky Bus from Disco Zoo, around 25% of an Undertale battle (Sans's fight), a fractal renderer, a recreation of Atari's Pong, and as I type this, I am working on the implementation of the concept of collision between the cursor and pixels read from a png file mapped to on-screen coordinates (like a maze).