Adapted from wikipedia:
The C&S Red Book is a trademark of Gamestuff Inc. and is an edition of Chivalry & Sorcery (C&S). It derives its name from the red cover of the 1st official (commercial) edition. The C&S Red Book's first edition is the only authorized version, even though its current legality seems to be in question. This version features a unique cover.
The unauthorized, second and later editions of The C&S Red Book are named in addition to being numbered: Phoenix (2nd), Chimera (3rd), Gorgon (4th), Manticore (5th), Hydra (6th) and Minotaur (7th). These feature slightly modified reproduction covers from the original release.
The C&S Red Book preserves the cover and typeface of the 1st edition of C&S.
All editions of The C&S Red Book have been made available as free downloads from a variety of sites.
Chivalry & Sorcery: World of the Troll-Head is a similar but separate effort, often considered a "fork" from Hydra (6th); it has been published in at least two revisions.