Ugopwn is an exploit for the DSiWare game Flipnote Studio.
You can use Ugopwn to load homebrew software. The exploit is rather inconvenient because you have to paste the first flipnote's page into the second flipnote 122 times. Thankfully, there is a much easier exploit called "Flipnote Lenny" that just requires you to copy one page and paste it into another page. Easy, right?