A fort defense game written in lisp in 30 days.
Common Lisp C#
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Bourtange is a game where you defend a number of planet-bases from a never ending onslaught of bad guys. Destroying intruders builds up your supply of resources, which in turn can be spent on new weapons and cores (the canonical base element).


  • r - reset the game
  • p - pause the game
  • 1 - restart game with core-blast
  • 2 - restart game with decoy
  • 3 - restart game with lifer
  • 4 - restart game with repellor
  • $ - give yourself more resources (cheat)
  • mouse click/move - buy cores and place them on the screen or buy weapons and place them on your cores


Each weapon costs a different amount of resources, depending on how useful that weapon is. Each time you buy a weapon, the cost of that weapon increases. There is no limit to how expensive a weapon can get. Some weapons take damage from enemies, other weapons take damage from time, but all weapons die (and renew) after some interval. After a weapon dies it goes into a cooldown period in which it is recharged for another round.

  • core blast - The core blast is cheap and weak. It is a good defense against small enemies (of which there will be many).
  • decoy - The decoy is a body shot out from the core that travels on a spiral path. It attracts enemies away from the core (hopefully) and out into space/computer tubes unknown.
  • lifer - The lifer gives its life to the core. Then it dies. Then it recharges. Then it gives life back to the core.
  • repellor - The repellor acts as a gravity shield, it temporarily banishes incoming baddies to the nether regions of the screen.


sbcl --load start.lisp

// i'm not sure how to do this in clisp