Nintendo WiFi Connection web root
On connecting to a network, a Nintendo gaming console (eg: DS, DSi, 3DS, Wii) will attempt to contact a server at http://conntest.nintendowifi.net/
If this fails at all, or results in a non-200 error code, the connection test will fail and the device will not connect to the network. You won't even be given a prompt to login to a captive portal.
How to work around this is by running a local copy of the site, then using DNS spoofing to host the page locally.
It doesn't effect any other functionality of the Nintendo device. Devices with a web browser (all bar the DS, which requires the Nintendo DS Browser game cartridge) can then log in to the captive portal directly on-device.
The page here should be an exact replica of the real connection test page, for compatibility reasons. I've done some tests with hex-edited ROMs in the past, and pointed it at a different URL (to work around issues with other captive portals) and it has worked, however I have no idea if there's other games out there that rely on the content of this page.