Andy Watkins offers a set of free wargames rules for the Wars of the Roses.
Charge Yr Pikes is a set of free wargames rules for the English Civil War. The authors write:
This set of rules is considerably modified from the first edition, which was in turn a modified version of CAVALIERS AND ROUNDHEADS’, by Gygax & Perren. These modifications were based on general dissatisfaction with the parts of the first edition that contrasted most with the “Brom Standard” rules which were introduced to our club by Larry Brom. The later editions (3rd, 4th and this one) are merely attempts to “fine-tune” the second edition.
MAWS offers a set of free wargames rules for the English Civil War. They’re meant for 25mm/28mm figures wehre one figure equals 10 men
Pike And Shot is John Armatys’ set of free wargames rules for fighting battles of the English Civil War. The rules also can be used to resolve battles of other 17th Century Western European conflicts. The rules set appears designed for 15mm figures, but has special instructions for using 25mm figs.