Hi its me. Hello :)
I have a 3DS Test Unit, which is capable of installing 3DS/DSi applications compiled in the .cia format from an SD card. So while a way to install applications you create yourself, for normal 3DSs is not possible (i.e. homebrew for 3DS is not yet possible), I am willing to test them for you. If you do make any applications you want me to test, send them with an email with a description of what the application is suppose to do and any instructions necessary. And if you want I can send screenshots and feedback (as detailed as I can) I make about the applications you or others may send. You can send them to "firstname.lastname@example.org".