Virtual Console

While Xbox Live Arcade and Playstation Network decided to focus mainly on new games, Nintendo originally decided that they should put their 20-year game backlog to good use, and got former rivals Hudson, SNK, Commodore, and even former Arch Enemy Sega on board for it.

The games on the service for the Wii came from these systems (more will hopefully be added later):
 * Nintendo Entertainment System
 * Super Nintendo Entertainment System
 * Nintendo 64
 * Sega Master System
 * Sega Genesis
 * TurboGrafx-16
 * Neo Geo
 * MSX in Japan
 * Commodore 64 in North America & Europe
 * Arcade Games via Virtual Console Arcade

The games on the service for the Nintendo 3DS came from these systems (more will hopefully be added later):
 * Game Boy
 * Game Boy Color
 * Game Boy Advance
 * Sega Game Gear
 * Nintendo Entertainment System (Originally exclusive to Ambassadors, and some games still are with this number having decreased slightly as of 2012, but as of the release of Super Mario Bros to non-Ambassadors it's one of the main systems, and the release of Punch-Out!! Featuring Mr. Dream, which was not an Ambassador game, showed that the games Ambassadors received are not the only ones planned for release)
 * TurboGrafx-16
 * 3D Classics (A series of past games from the NES, SNES, and even Arcade games that have the ability to be seen in 3D; these are mostly based on games originally developed by Nintendo itself aside from the occasional game licensed from another company.)

If Nintendo's Author's Saving Throw following their surprisingly early price cut for the Nintendo 3DS is anything to go by, then the Game Boy Advance should join these systems soon.

Essentially, the Virtual Console was console game emulation made legal and had the backing from every major console post-Gamecube manufacturer there ever was besides Atari, Sony, Microsoft, and some other failed consoles that Nintendo doesn't want to bother with. It was successful enough that it led to Wii Ware once Nintendo decided to offer original downloadable software for the Wii.

One really cool benefit was the arrival of games not available in other regions, such as Sin and Punishment and PulseMan, the former of which got a sequel because it sold so well on this service, in all the regions.