Oxyd

Oxyd itself was a sequel to a lesser-known game, called Esprit.

The Oxyd series is no longer maintained by Dongleware.

The Oxyd series had a quite unique marketing method: the entire games were free to distribute, thus being easily obtainable from shareware-CDs or bulletin boards. The first ten levels could be played without restrictions. From the eleventh level onward, at various intervals throughout the games, so-called "Magic Stones" blocked crucial parts and passageways of the landscapes, mostly rendering progress impossible. These stones could only be removed by entering a code. A code book called the "Oxyd Book" was sold separately for the price of a budget video game. This book contains approximately 150 pages of code tables matching the information given on the Magic Stone. This form of software protection is effectively using the book as a dongle; however, unlike other games which use the code book protection approach, the game itself was free.