Why are there so many nightly builds? Which one should I use?

Names are in the format: ohrrpgce-wip-GRAPHICS-MUSIC.zip

GRAPHICS = fb = FreeBasic graphics. This is the default
GRAPHICS = sdl = Simple Directmedia Library
GRAPHICS = alleg = Allegro Game Library

MUSIC = native  = Audiere + Windows MIDI
MUSIC = native2 = Audiere + Windows MIDI (alternate implementation)
MUSIC = sdl     = Simple Directmedia Library
MUSIC = allegro = Allegro Game Library

If you are not sure which version to use, try ohrrpgce-wip-default.zip