A quick Google shows that it's a Wii homebrew loader.
I'll try and do some looking into it, but I'm not a Wii guy by any means, so I might not come across anything.
Update.
via
http://wiibrew.org/wiki/Gecko_OSGecko OS is an application to allow the running of Import games and cheat codes.
I tried to do some looking, and the best thing I could find was a few people suggesting "put Gecko OS Mod on, and if Gecko OS fails to load, then Gecko OS Mod will load".
Mods: Move this to the Wii section?