Maelstrom
Last published by Puffin Books in 1984, this cult classic is now available under license as a pdf. Written by Alexander Scott when still at school, this is a classic no modern gamer can be without. This is no low-quality scan, but a re-created book, complete with every fantastic illustration from the original.
While the books background sets the game in 16th Century England, this fast but powerful system allows you to create, and adventure with, Nobles, Mercenaries, Priests, Tradesmen and Herbalists across any historical setting.
The innovative freeform magical system, arguably a precursor to such classics as Ars MagicaTM, allows Mages to warp reality to their own ends. Combat is fast and furious, with dozens of weapons and armours, and the wound system means that injuries are a real threat.
Includes full character generation rules, a solo adventure, an extensive (and much copied!) herb guide, a short scenario, advanced rules and much more, as well as dozens of illustrations, all in more than 300 pages.
You can purchase Maelstrom from RPGNow.