If you're not familar with .mod format, you should read up on it, because they're an efficient way to store music. Instead of recording a full waveform, like mp3/aac, they store a number of short samples and a score file for the music.
Having mod-playing code on a platform is extremely useful because it allows that platform to play songs with very limited resources - which is often the case in embedded environments where DSP is most useful.
The Bitbox itself is a DIY video game console based on the excellent stm32f4 processor. So, having the mod player there is valuable because it will let you add music to your video games without having much memory and disk space. Speaking of disk space, this release of the mod player is extra great because it can play the mod files directly from an SD card! So, check it out!