It's a rom, homebrew, skin and firmware manager for the R4. Basically you can build up a game, homebrew and firmware library by dropping them into it and then build a list of the stuff (MP3, OGG and DPG as well) you want to add to the card by using lists or drag and drop. Then when you're happy with the list you can tell the program to copy it to the card.
You can add skins to the card by browsing folders with either archives or the bmp files for skins.