RTOS System-6 - asm-written RTOS.
PascalOS - pascal-written OS-skeleton.
FontLib - antialiasing micro-library.
nanoView - small HTML-to-Text library.
inView - small and simple image viewer.
WinKAR - small LZMA\LZO\LZW archiver.
fmad_mp3.zip - FASM-rewritten MAD MP3 decoder (integer decoder) with full source code. Just for example. MP3 file included in play.exe. Play.exe producec output .wav file. WAVE header hardcoded for this only MP3. So, You need to recode JUST play.asm for Your needs. All OS-depended code in is code.SYSTEM.inc and play.asm - so it's very portable.
MP2 nanoDecoder.zip - FASM-written MPEG1 LayerII to WAVE decoder. With full source code included.