Nintendo Wi-Fi Connection

Nintendo Wi-Fi Connection, or WFC, was a service from Nintendo that allowed Nintendo Wii and Nintendo DS games and applications to connect to the Internet. Super Smash Bros. Brawl was one of the many games that had compatibility with the service, using it to allow for online brawls either with friends or with anyone; in addition, players could also exchange some data with other players with the service.

The service was later superseded by the Nintendo Network for the Wii U and 3DS, though the Nintendo Wi-Fi Connection continued to act as a legacy connection for the Wii and DS consoles; both the Wii U and 3DS had only limited compatibility with the service. With the shutdown of the network provider, the service went permanently offline on May 20th, 2014. However, thanks to hacks, particularly Wiimmfi, players can continue playing compatible games via private servers, and the emulator Dolphin also supports online play for Brawl, along with other benefits.

In Brawl
The Nintendo Wi-Fi Connection allowed players to play against each other online for the first time in the series. A primary point of interest was that it allowed players to either play with anyone in the world or with registered friends. The former, With Anyone, allowed players to either take part in standard free-for-all battles via Basic Brawl, or to play as a part of a team in Team Battle. The latter contained an almost fully customizable ruleset, which allowed websites such as All is Brawl to be formed with the aim of adding competition into the mix, spawning an online scene for competitive Smash as a whole.

In addition to allowing for online gaming, Brawl also allowed players to send replays, custom stages, and snapshots to other players with whom they had registered. An applied use of this was the Smash Service, a free service that sent players a replay, a custom stage, and a snapshot each day; these pieces of data came from submissions of players and were deleted at the end of the day.

Fan replacements
Wiimmfi is a fan server that makes WFC usable after the official servers were shut down.

AltWFC also exists, but is less popular.