Supaplex is now freeware thanks to the auspices of Digital Integration, copyright holder and original publisher.
This game has a native Windows version, and can be played in browser (please see the links section below).
Unlimited red discs: Get one red utility disc. Activate it, then quickly move up, down, left or right. Return to your original location and take the disc. Move away as quickly as possible. If done correctly, you will be able to use the disc again.
Level skip: Note, this requires using a hex editor. If you don't know what that is, this cheat probably is not for you. Edit the savefile with a hex editor (it's a hidden file!) and edit it after your name (as you entered when you first created a character in the game). Enter a few 01 hex characters (ASCII code 1, a small face). Each one you enter counts as one more completed level. Keep adding more to skip more levels.
Description by VGTips