NGGTool
"Neo-Geo Graphic Tool Suite" by evo.
Found as an archive including 4 executables and a text file.
Decode.exe and Recode.exe are used for sprite tiles, decode8.exe and recode8.exe for fix tiles.
The decoders take two C ROMs or one S ROM and output a 4BPP SNES planar type file compatible with YY-CHR and Tile molester. Recorders do exactly the opposite.
Warning
It seems recode8.exe is broken, it inverts some color indexes:
Normal Converted 0 0 1 1 2 2 3 5 4 3 5 7 6 9 7 B 8 4 9 8 A A B C C 6 D D E E F F
This isn't a problem when editing existing ROMs without knowing the palettes, but becomes one when importing converted graphics.