What it is:
DLDI is a Dynamically Linked Device Interface for libfat. Basically what that means is if a homebrew app is coded in FAT, in can be patched to be compatible with your specific device if a DLDI has been released by the manufacturer.
Where to get it:
Chism has a DLDI page with all of the released libraries in 1 place.http://chishm.drunkencoders.com/DLDI/
What to do:
1st download the Patching Software (dlditool) for your PCs OS. I use WinXP so I downloaded the Win32 GUI, there are also Linux and MacOS X patchers available.
2nd download the DLDI Device Patch for your device. I have a DS-Xtreme so I downloaded the DS-X DLDI (dsx.dldi).
3rd download the homebrew app to be patched. In this case I patched DSOrganize 2.5http://www.dragonminded.com/?loc=ndsdev/DSOrganize
Extract the DLDI patcher and patch to the same directory.
For Example - C:\NDS\dlditool-win32-gui\
Extract the Homebrew Application to be patched to a different directory.
For Example - C:\NDS\DSOrganize_2_5\
Now open the patcher tool (C:\NDS\dlditool-win32-gui\dlditool32.exe).
Click the 3 dots and browse for your dldi. It should be in the same directory as the patcher tool (C:\NDS\dlditool-win32-gui\dlditool32.exe).
Click the 3 dots to browse for your binary file (nds) file.
If your screen has both fields filled in correctly, you are ready to patch. Click the Patch button.
If everything finishes correctly, you will see 'Patched Successfully' in the dialog box.
Good job! Copy the newly patched app and its accompanied files to your device. In this case I copied the 'DSOrganize' folder to the root of my DS-X and moved DSOrganize.nds to the 'Apps' folder.