Tutorials and guides

Gateway:
http://pastebin.com/MktNaDSm
http://www.maxconsole.com/maxcon_forums/threads/286487-3DS-N3DS-Gateway-Ultra-Guide
https://www.youtube.com/playlist?list=PL1CadovfabPtTXpw4iC_R9MiLMdLOZS3h

Sig-patched CFW guide:
http://pastebin.com/GpeAjJPW

How to boot rxTools CFW using a smartphone instead of internet connection:
http://pastebin.com/iD87w3H8

How to boot rxTools via MSET exploit:
http://pastebin.com/n5WszvNF

Using SaveDataFiler:
http://pastebin.com/T6ZRxPYW

Downgrading:
http://www.maxconsole.com/maxcon_forums/threads/286618-GUIDE-Downgrading-your-3DS-from-4-5-9-2-down-to-4-x
http://gbatemp.net/threads/guide-the-emunand-save-data-mega-guide-gbatemp-doesnt-deserve.378491/

Downgrading your emuNAND browser to an exploitable version (Doesn't work with N3DS):
http://pastebin.com/tV5q95xr

Converting 3ds to CIA:
http://gbatemp.net/threads/tutorial-converting-3ds-to-cia-for-dummies.373722/

Installing CIAs:
http://www.maxconsole.com/maxcon_forums/threads/285969-BigBlueMenu-and-CIA-files

Converting .3ds to .3dz to play online:
http://gbatemp.net/threads/scene-roms-online-tutorial-for-dummies.370589/
http://www.maxconsole.com/maxcon_forums/threads/284944-How-to-play-online-TUTORIAL!!!-And-all-things-online!!!

Downgrading without Gateway and installing CFW:
http://gbatemp.net/threads/tutorial-from-9-2-or-any-lower-firmware-to-cfw-4-5-without-gateway.378371/