Wiikey U is the first and only optical drive emulator that allows you to play all your WiiU games from any USB media!
Wiikey 1 was launched in 2007 to much commercial acclaim and is probably the most popular (and most plagiarized!) mod chip of all time. It was compatible with all Wii consoles at the time (DMS aka D2A and D2B). It was the first chip to be fully updatable by DVD, and the only chip from the first generation to receive an update for the last protection that was introduced for Wii, ie the BCA check on New Super Mario Bros.
Wiikey 2 was launched in 2008 for newer Wiis that were not compatible with Wiikey 1. In addition to being updatable by DVD it also had recovery mode and an on-screen menu for configuration. It was compatible with DMS/D2A, D2B, D2C, D2C2 and D2E drives.
Drivekey was launched in 2009 as a solder-free solution, also to much popular and commercial acclaim. In addition to the D2* models it also supported D3.
Wiikey Fusion was launched in 2010 and added support for loading games from SD cards. It was compatible with all Wii models (although the latest ones only supported loading games from SD).