Ironhax is an exploit in the USA/EUR eShop game "IronFall: Invasion" that allows people to load 3DS homebrew on system versions 9.5-9.9. "IronFall: Invasion" is not available for download anymore as it was removed from Nintendo eShop as of August 11th, 2015, so a previously downloaded copy is necessary in order to use the exploit. Unlike other exploits this is a secondary exploit, meaning in order to install it the use of another exploit with the Homebrew Launcher is required. The Ironhax installer requires internet, afterwards the installed exploit will work without internet.
Download Ironhax Installer: Ironhax Installer
Setup instructions available here: 3DS homebrew official site (scroll down to the IronFall section down the page).
Like other exploits, Ironhax will launch boot.3dsx from the root of the SD card so make sure you have the Homebrew Launcher which is included with the 3DS homebrew starter kit which is available here: 3DS homebrew starter kit
Sometimes the 3DS might get stuck at a blue screen or a white screen (bottom touch screen) and if this happens force shut your 3DS down by holding the power button until the blue light turns off and then try the whole exploit again.
Also keep in mind that Ironhax is a Userland exploit, meaning that it has only ARM11 access and doesn't have kernel. This means we can't modify the system but that doesn't mean we can't do some awesome homebrew! Regionfree, emulators, custom homemenu themes, playcoin hacks, etc. are all available!