Jailbreaking your 3DS is not synonymous with piracy, no matter how popular it may be to do so for that end. Here's a non-exhaustive sampling of some cool things you can do with your fancy little 3D clamshell computer.
- If you've got a New 3DS (or New 2DS), here's how to play 3D (or 2D) videos at 60FPS at the 3DS' native screen resolution! https://github.com/Core-2-Extreme/Video_player_for_3DS
- Use the hardware GBA backwards-compatibility for any game, originally only available for "3DS Ambassador" titles. https://github.com/profi200/open_agb_firm
- If you're a GBA homebrew developer, setting up your 3DS with https://github.com/joshbackstein/gba-net-boot is a great way to test on GBA hardware as part of your workflow without fiddling with a flashcart and causing contact wear. (This is a godsend while iterating on timing-sensitive demoscene bullshit that's inconsistent in emulators)
- Speaking of cartridge wear, you can install your own gamecards to your internal memory so you don't have to juggle them. https://github.com/d0k3/GodMode9
- Back up your game saves! https://github.com/BernardoGiordano/Checkpoint
- Use a Gamecube/Xbox controller to play 3DS games! https://github.com/MissingNO123/GCIR
- You can target the 3DS with Rust! https://github.com/rust3ds
game ports!
- Half-Life
- Sonic Mania
- Old Minecraft
- 3D Pinball Space Cadet
- Friday Night Funkin
- Transport Tycoon
- Tomb Raider
- Higurashi
computer's!
- Native Linux with Wayland (Weston)! https://github.com/linux-3ds/linux/wiki
- Mini vMac https://github.com/TaraHoleInIt/minivmac-3ds
- DOSBox https://github.com/MrHuu/dosbox-3ds/
pretend computer's!
- uxn https://github.com/asiekierka/uxnds
- PICO-8 https://github.com/jtothebell/fake-08
- TIC-80 https://github.com/asiekierka/TIC-80
emulators
(you've got a Retrode, right?)
- Nintendo 64??? https://github.com/masterfeizz/DaedalusX64-3DS
- SNES https://github.com/Arisotura/blargSnes
- Megadrive(/CD/32X) and NES https://github.com/bubble2k16/emus3ds
mods????
(these will work on legitimate copies of games; the patching is done at runtime, i.e. by redirecting I/O to the patched assets)
- MM3D: Un-nerf Zora swimming and many other improvements https://restoration.zora.re
- MK7: Custom Track Grand Prix 7 https://ctgp-7.github.io/
- YNI: Old (non-kazoo) music https://old.reddit.com/r/3dshacks/comments/8c6x0x/release_yoshis_new_island_music_improvement_10/