3DS

All systems can be hacked easily. Updating to the latest system version (11.17.0-50, May 23, 2023) is not recommended for old 3DS models.

If you don't have a 3DS yet: https://pastebin.com/cqM33rKH

If you have already hacked your 3DS before, scroll to the bottom of this page to check if your setup and homebrew software are up to date.

[start here] 3DS hacking guide: https://hax.b4k.co/3ds/guide

Troubleshooting: https://troubleshoot.uwuu.ca

If you want a game or other software, download its .cia file and install it using FBI. You don't need to keep the .cia file after installing it.
If you have a direct download link, you can download + install the game directly on your 3DS through FBI by typing in the link or scanning its QR code (create it with https://www.qr-code-generator.com).
You can also use Boop on your PC to make game installation easier. https://github.com/miltoncandelero/Boop#boop
Other than .cia, homebrew software is also distributed in .3dsx format, which you can run using the Homebrew Launcher.

Game downloads
https://hshop.erista.me (has QR codes that can be scanned directly in FBI)
https://r-roms.github.io/megathread/nintendo/#nintendo-3ds
https://www.ziperto.com (includes prepatched fantranslations, undubs and uncensored games)
https://ciaspara3ds.blogspot.com
https://www.cia-3ds.com
https://pastebin.com/jxPF1E5E (this pastebin is old, but you might find some links useful)

Using adblockers and Universal Bypass is recommended.

open_agb_firm (play GBA games)
https://github.com/profi200/open_agb_firm

TWiLightMenu++ (play DS/DSi games without a flashcard)
https://gbatemp.net/threads/472200

.cia forwarders for TWiLightMenu++
https://gbatemp.net/threads/426174

DS games in widescreen
https://gbatemp.net/threads/543212

Extra filters for DS games
https://gbatemp.net/threads/542694
https://gbatemp.net/threads/542694/page-9#post-8712553

Custom serves for DS online
https://www.youtube.com/watch?v=Sh0AZR-tKwM


Scene releases
http://3dsdb.com

Recommended games
https://img.fireden.net/vg/image/1536/89/1536896679124.jpg (broken link, sorry)


CTRPluginFramework (fast screenshots and cheat engine)
https://pastebin.com/YNb7J1Ue

Save managers
Checkpoint: https://github.com/BernardoGiordano/Checkpoint/releases/latest
JKSM: https://github.com/J-D-K/JKSM/releases/latest

Emulators
RetroArch: https://docs.libretro.com/guides/install-3ds2ds
DaedalusX64-3DS (Nintendo 64): https://github.com/masterfeizz/DaedalusX64-3DS/releases
PCSX Rearmed full speed guide: https://www.reddit.com/r/3dshacks/comments/jvkotb
Virtual Console injection: https://gbatemp.net/threads/371894
More information: https://emulation.gametechwiki.com/index.php/Emulators_on_3DS

While there are GBA emulators for the New 3DS, GBA games can be played natively through open_agb_firm or Virtual Console injection.
DS software also runs natively, including TWiLightMenu++.
RetroArch has a collection of emulators for several different consoles. Those emulators also have standalone releases. Due to the improved hardware of the 3DS, some emulators perform better on there rather than on the older models. SNES games run fine on the New 3DS. If you want to play SNES games on the original 3DS, Snes9x is recommended.

Universal Updater
https://github.com/Universal-Team/Universal-Updater/releases

3DShell (file manager)
https://github.com/joel16/3DShell#3dshell--

FTP transfers from PC to 3DS SD/micro SD card
https://github.com/mtheall/ftpd#ftpd

3DSBank (if you want to install more than 300 titles/games)
https://github.com/RocketRobz/3DSBank

Custom HOME Menu themes
Download site: https://themeplaza.eu/themes
Anemone (theme installer): https://gbatemp.net/threads/482804
Howling Theme Tool (.cia creator): https://gbatemp.net/threads/401081
Usagi (theme creator for Windows): https://gbatemp.net/threads/412233
Kame (theme creator for Linux and OSX): https://gbatemp.net/threads/542943
YATA+ (theme creator): https://gbatemp.net/threads/379209
Custom badges: https://pastebin.com/RhDJewxW
Advanced HOME Menu customization: https://axities.github.io

Guide on how to decrypt, extract and rebuild 3DS/CIA/CXI files
https://gbatemp.net/threads/383055

Pretendo (Work in progress Nintendo Network replacement for custom servers)
https://pretendo.network

Flipnote Studio 3DS and DSi online
http://kaeru.world

rverse (Miiverse replacement)
https://twitter.com/rverseclub

CTGP-7, a huge Mario Kart 7 mod
https://gamebanana.com/gamefiles/7946

PKSM, free offline Pokémon Bank, events injector and save editor. For gens 4, 5, 6 and 7
https://github.com/FlagBrew/PKSM/releases


Freeshop and the titlekey website don't work anymore and they can't be fixed.
Some DS flashcards, known as time bombs, stop working if the console is set past a specific date. Avoid buying those.  TWiLightMenu++ (https://gbatemp.net/threads/472200) and/or R4i+ 3DS/DS RTS (https://www.nds-card.com/ProShow.asp?ProID=575) are recommended instead. TWiLightMenu++ is homebrew software that allows you to play DS games without a flashcard. It can also be used along with a flashcard.
Follow this if you've made a save backup using Nintendo's official tool and the save backup no longer works. https://gbatemp.net/threads/455183/#post-8313552
Luigi's Mansion needs a locale fix, which can be done using Luma Locale Switcher. https://github.com/Possum/LumaLocaleSwitcher#lumalocaleswitcher

CFWs like Gateway, Blue3DS, rxTools, reiNAND and CakesFW are outdated. Any setup that involves a "3DS flashcard" or EmuNAND is outdated. Install Luma by following the "start here" guide.
Game installer Devmenu/BigBlueBox is outdated. Use FBI.
Cheating methods involving NTR CFW, Gateway's cheat feature and the AR code web browser exploit are outdated. Use CTRPluginFramework or Luma's rosalina menu (press L + down + Select to open).
Save managers like SaveDataFiler, TWLSaveTool, Datel Action Replay PowerSaves and CyberGadget are outdated. Use JKSM or Checkpoint.
HOME menu theme managers like CHMM and CHMM2 are outdated. Use Anemone.