Retro Invaders is a complete, sellable fixed-shooter in the classic arcade style: an 11 x 5 formation that marches, drops and speeds up as you thin it out, four shield bunkers that crumble pixel by pixel, a mystery UFO, three bomb types, 30 data-driven waves with new alien types and a boss every fifth wave, four boss fights, power-ups (rapid fire, spread shot, shield bubble, slow-time, smart bomb), a kill-streak multiplier and extra lives. One config and an Options menu switch between two presets: Retro (1-bit pixel sprites, CRT scanlines and curvature, stepping four-note march, chiptune sound) and Modern (smooth Kenney-based art, bloom, particles, screen shake, parallax star fields, dynamic music). Modes: Classic, Endless, seeded Daily Challenge, 2-player Co-op and Alternating, with an attract-mode demo, arcade name entry, local hi-score tables, saved progress, three difficulties, keyboard, gamepad and touch controls.

Waves, aliens, bombs, bosses and power-ups are .tres resources. Accessibility (colour-blind modes, reduced motion and flashing, big text), English / Spanish / German localization, 22 achievements with optional GodotSteam hooks (App ID 480 test) and a 548-check smoke test where a bot clears all 30 waves are included. Everything is CC0 with every file's source documented (Kenney, Juhani Junkala and other OpenGameArt authors plus original generated art).