1nvas0r is similar to 1nvader (both the C64 and Atari versions), with the same thing: one alien invader at a time, firing base constantly moving, base switches direction when firing a projectile. What makes 1nvas0r unique is that it was part of a Basic 10-liner contest; the source code is actually 8 lines long in Atari FastBasic (with up to 256 characters on a line).