Gravity Gang soundtrack. All tracks are CC0 (public domain) from OpenGameArt.org.
Trimmed, loudness-normalized and re-encoded to 96 kbps MP3 for the web.

dust.mp3    "Desert Theme" (Caravan) by yd                 https://opengameart.org/content/desert-theme
selene.mp3  "Another space background track" (Observing The Star) by yd   https://opengameart.org/content/another-space-background-track
umbral.mp3  "Creepy Forest" by haeldb (CC0 option)         https://opengameart.org/content/creepy-forest-f
tide.mp3    "Underwater Theme" by Cleyton Kauffman         https://opengameart.org/content/underwater-theme
arena.mp3   "Battle Theme A" by cynicmusic                  https://opengameart.org/content/battle-theme-a
boss.mp3    "Epic Boss Battle" by Juhani Junkala (SubspaceAudio)  https://opengameart.org/content/boss-battle-music
frost.mp3   "Snow Theme" (bgm_snow_theme_loop) by Cleyton Kauffman   https://opengameart.org/content/snow-theme
hub.mp3     "Gravity Turn" (calm) by vitalezzz              https://opengameart.org/content/gravity-turn
vault.mp3   "sector" by SRG774                               https://opengameart.org (CC0, sector_0.mp3)
vault2.mp3  "pulse" by SRG774                                https://opengameart.org (CC0, pulse_0.mp3)
keeper.mp3  "Heavy Boss Battle 1" by MintoDog                https://opengameart.org (CC0, heavy_boss_battle_1_bpm200.mp3)
mission.mp3 "Fast fight" by Ville Nousiainen (Xythe)         https://opengameart.org/node/30344
galaxy.mp3  "Outer Space Loop" by wipics                     https://opengameart.org/content/outer-space-loop
arena2.mp3  "Heavy Dungeon" by MintoDog                      https://opengameart.org (CC0, heavy_dungeon_bpm160.mp3)
menu.mp3    "To Be Continued" (orchestral) by Bobjt, used under its CC0 option   https://opengameart.org/content/to-be-continued-orchestral