December update:

Animations (by Pedro Caetano)

Sounds (by Pedro Caetano)

Background music (by Catarina Pereira on BeepBox)

Changes to the splash screen, win and game over screens

Retro font (8-bit pusab by Seba Perez)

Retro mouse cursor (by Pedro Caetano)

Change of selection highlights

Maybe I'll add a level creator in the future, but the python code is easy to change to create a new level.