Xsystem is a filebrowser by hacker013.

Release notes:

I’m busy with a semi os / filebrowser. It is like DS-DOS, this is in early alpha stage.
Know bugs: Keyboard is not drawn properbly.
It includes a Brainfuck interpreter (it supports all 8 commands + exit sign X.)
Enter help to see all commands. Please give good feeadback.

http://forum.gbadev.org/viewtopic.php?t=16084