Version 1.1 - Reworked code and squeezed in invader animation
Version 1.2 - Invader shots now target player, tweaked barriers, fixed disappearing score glitch
This is a port of the original arcade Space Invaders in just over half a kilobyte. I had to simplify a few things, like only having one invader type, cutting the UFO, and rethinking the lives system a little bit, but most of the major elements are there, and I think it plays fairly well.
Features:

Score system
Level Progression
Enemy Animation
Enemy Fire with homing shots
Destructible barriers
Increasing invader speed and fire rate as number destroyed increases
Damage system (your laser cannon changes colors after taking a hit, and will be destroyed after 3)

Controls:
LR----Move laser cannon
ZX----Fire

License: None (Free)