In the late summer of 2000, a group called "Sega Extreme" dumped the May 10th beta of Sonic CD. This beta that was dump was of an earlier version to Stealth's copy and contained some very interesting differences to the final version. The beta was then posted online in the form of an ISO image. However, the ISO image was only online for a short time and was taken down just a few hours later. Luckily, A.J. Freda of SSNTails.org and Kaervek of emumania.com, among possible others, managed to download it in full before it was taken down.
On this website, you will find information on the beta version of Sonic CD ranging from information about the beta version of the game to instructions on how to burn it and emulate it. There is also a compatibility list to give you an insight as to what versions of the Mega CD/Sega CD the game runs on. Last but not least, the Sonic CD beta image file can be downloaded from the "downloads" section. The file is only about 6 Megs rar'ed, which makes it fairly practical for the average 56k modem user.
Update: 08/13/2001. Part two of updates to the site. The differences pages for Collision Chaos and Tidal Tempest are up.
Update: 08/11/2001. Part one of updates to the site. The Emulators available section is up and my email is on the page if you need it. More additions will be made over the following days.
Update: 06/11/2001. More changes and additions. The two player cooperative mode cheat has been added as well as the introductory paragraph edited by Andy.
Update: 06/10/2001. Corrected some stuff on the site. Added Level Select and Debug cheats in "The Other Zones" section. I have also added the section on how to emulate the game.
Thanks to A.J. Freda for the high-colour Sonic image.