MAME Wii, a Wii port of the popular SDL MAME arcade emulator.

Here's the changelog and some developer notes for version 0.3:

0.3 - October 29. 2009

• Added support for many more ROMs
• Fatal errors are now logged in errors.txt
• More default control changes

• Fixed rom selection bug
• Changes to the layout of the configuration files to make it more like other Wii homebrew

• Lots of ROMs are supported, but not all of them. If you don't see the ROM in the list in the emulator, then support for that ROM isn't included. This is to keep the size of the emulator low enough to run effectively on the Wii. A list of all the ones that are can be found here: http://www.toadking.com/wiimame.txt
• Just because a ROM is supported does not mean it will run. Even games for early boards like CPS-1 can fail to run due to RAM limitations. If the emulator suddenly kicks you out to the Homebrew Channel, look in the MAME app folder (/apps/MAME) for a file called errors.txt. If it says something about failing to allocate space, then odds are the ROM can"onclick="return FollowLink(135596)">
  
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• Only software rendering is supported. This makes playing games without using the frameskipper slow, but the auto-frameskipper feature is enabled by default.
• No USB support yet.
• Stereo audio is disabled.
• The joystick on GameCube controllers can't be used.
• The default UI font is way too small. A custom font is included, called Helvetica LT.

• SDLMame 0.125 on Wii (UPDATED) - fixed random resets for smaller ROMs

Via WiiBrew