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For When You Need To Backup Those Saves
(i.imgur.com)
The Open Source Cartridge Reader is a great diy project for dumping your own roms and saves. If you order a kit with the surface mount components already installed, it's also a great beginner soldering project.
Once I extracted my Fire Emblem 7 GBA cartridge's save to keep stuff I had unlocked and play it elsewhere.
It was easy, I didn't need any special hardware beside a DS and a flash cart, and a bit of homebrew software.