The Sega Meganet reference article from the English Wikipedia on 24-Apr-2004
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Sega Meganet

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The Sega Meganet was a network service in Japan for people using the Sega Megadrive.

To connect, players had to use a modem made for the video game console. The modem and service were only released in Japan.

With the console, subscribers downloaded small games and played them over a network with people across Japan.

Some of the games included Phantasy Star II text adventures, Sonic Eraser (a Sonic the Hedgehog puzzle game), and a Mahjong title.

The Sega Meganet was not a success in Japan.