DualSlot Browser lets you copy and boot files to and from the filesystems available. That means if you have two FAT based flashcarts inserted, you will have access to both! With this boot feature you can boot into GBA mode or boot NDS homebrew files. The boot function Auto-DLDI patches for whatever filesystem its on. So if you boot a homebrew on the Slot-2 it will have access to the Slot-2 FAT. Also with the new MP3 Player feature you can build your own playlist or have DSBrowser search the available FAT for MP3s. All MP3s found will be added to a new playlist. MP3s can be played while exploring the apps features!

Changes:

-Updated GUI: Can now load backgrounds and settings from FAT
-Removed DLDS files: Can now read DLDI from FAT
-Added support for AKRPG NAND: If you have an AKRPG just boot from the SD and you will have access to both
-Added option to boot into GBA mode
-Changed/Added some controls
-Added support for MP3 playback
-Added file size display
-Added multiple copy/delete support
-Added display of copy speed
-Added display of current date and time
-The file list is now sorted alphabetically
-Renaming works now by copying file and deleting source
-Booting now works on the extra FAT systems
-Fixed pause when lid closed
-Fixed compatibility with M3/G6 Real
-Various other bug fixes

http://forum.gbadev.org/viewtopic.php?t=14630