WW1
1916
World War I rules from The War Times Journal.
1930
1930! is a game that requires 5 players and you each take leadership of one of the major powers of the time Great Britain, Germany, France, Russia or Italy. There are also a number of (initially) neutral minor powers countries such as Spain, Belgium, Ireland.
A Spanish Crossfire
This is a variant of Crossfire for early 20th century wars
involving the Spanish , notably the Spanish
Civil War and Rif War.
These two wars are grouped together because Spanish Army of Africa was involved
in both.
Aces At Dawn
Aces at Dawn is a game of quasi-historical combat in the skies. As with all Majestic Twelve games, Aces at Dawn is fun and easy to play, works with any line of miniatures, and encourages players to use their imagination and have fun (Demo Version).
Air War : 1917
A stripped down free set of the new 2nd edition of our popular biplane era air combat rules AirWar: 1918.
Alienstar World War 1
For the period 1914 to 1918 using 2mm to 1/35th scale.
And Was Jerusalem Builded Here
A great fun (and perhaps slightly 'retro') set of rules for playing
fictional battles and skirmishes in 1930's Britain. Designed to
encourage players to add their own ideas and additions.
Battlefleet
Naval Wargaming rules for the turn of the century, 1895 - 1905. From the "War Times Journal".
Beyond The River Don
A campaign game that takes maybe 30 minutes to create from scratch, with limitless scenarios, a different map each and every time, and has counters representing the following armies and their equipment: Reds, Whites, Greens, Estonians, Latvians, Finns, Lithuanians, Ukrainians, Poles, Armenians, Turks, French, Greeks, Japanese, American, British Empire and Freikorps.
Blue Skies, Wood and Canvas
A set of World War 1 aerial combat rules adapted from the original "Squadrons" game by John F. Stanoch designed for 1/144 aircraft.
Canvas Eagles
WWI air combat miniatures game, sweep the skies free of the dreaded Fokker scourge! Lead the Flying Circus in a Jabo over the Allied trenches!
Coal and the Kaiser
This is a game of low to moderate complexity portraying tactical naval combat in the period from 1904 through 1918. 
Combat Wings
An air combat game set in the First World War. Each plane is different with its own aircraft’s characteristics with a series of specific manoeuvres and special abilities. 
Crossing The Wire
Divisional level game about trench warfare at Brigade and divisional level using historical maps and counters. Can also be used with 1/300 scale miniatures. Also Example counters for 29th British Division and Map of Beamont Hamel Battlefield for 1 July 1916.
Cuadro Golpeando
Spanish Civil War rules variant of Square Bashing.
Damn Battleships Again
This is a set of wargames rules for pre-dreadnought naval battles between 1890 and 1913 by Phil Barker.
Day of the Dreadnoughts
Fast play rules for The Battle of Jutland (1916).
De Bellis Horribilis
DBA for WW1.
Dogfight!
Homebrew rules for gaming with miniatures. These rules are an attempt to create for players a different experience in gaming WW1 aerial combat.
Dreadnought
Turn of the Century Naval rules, these rules are based heavily on the Silent death fighter combat rules. German Templates and British Templates available.
Dreadnoughts
Rules for naval warfare from around 1900 until airpower became dominant. They can be used for the Russo-Japanese war, WWI & the early part of WWII. Designed for ship models about 50mm long on a 75mm hex grid.
East Africa WWI
Company level rules for East Africa 1914-18.
Easy Ship
Simple naval-battle rules for 20th-century ships, especially my "All the Ships" counters. Minimal record-keeping and critical-hit-centered rules bring large battles into the realm of possibility, while preserving most of each ship's details.
Enfilade
A new set of skirmish rules under development by Ian Shaw. Covers 1914 to 2010.
Firepower
Naval wargaming for the period 1900 to 1945. 
Flanders Fields
A set of rules which allows players to war game actions from Regiment (Brigade), to Divisional level actions from the war on the western front between 1914 and 1918. They are a Beta version. 
Flying Circus
A quick and easy World War I air combat game, it is meant to cover air combat from 1915 through 1918. The game is based on Avalon Hill’s Mustangs game.
Fokker
Simple World War One Aerial Rules.
Forward Comrades
This is a revision of Jay Stribling's Russian Civil War rules Red and White with a different sequence of action.
From Mons to the Meuse-Argonne
A Storm of Steel supplement for World War 1. The core rules can be found here.
Harkas y Arma Blancas
Revised rules for The Rif War 1921-1927. 
Heroes of the (Russian) Civil War
Skirmish rules for small unit actions of the Russian Civil War. (Large file 25mb). 
Home Before The Leaves Fall
This Piquet supplement is designed to re fight large scale games of the early campaigns of the Great War. Included in these rules are 4 separate scenarios covering France, Galicia, Balkans and East Prussia and 2 scales Divisional and Corps. With these rules you will be able to recreate the Grand Strategic moves of the opening campaigns of 1914. 
Honour The Dead
Spanish Civil War these were written to make use of Peter Pig's fantastic 15mm range. 
Hordes in the Trenches
Hordes Of The Things variant for World War I. Join the yahoo group.
Impresa di Premuda, 1918
Naval wargame rules, Italian Language.
In Flanders Fields
Computer-assisted rules for large-scale games set during late WWI on the Western Front.
Instant Spandaus
These rules provide an abstract representation of air to air combat between WWI aircraft. They are designed to be equally suitable for solo as well as for two or more players. The scale is individual aircraft.
Ironclad Draughts
A simple set of ironclad rules on one page. 
I Wish I Was In France
Written to protray the interesting and different style of warfare in East Africa during the Great War, these rules were inspired by the Pendraken 10mm range. 
Jutland: The Rules of the Game
Rules for fighting very large scale WWI fleet actions with very small ships.
Knights of the Sky
WWI air rules by HMGS South’s own Ray Phillips. 
Landwehrmarine
Fast and easy rule pack for naval warfare during first half 20th century. Contain Atlantic, Pacific and Spanish Civil War fleet list. Spanish language. 
Linea di Fila
Large WW1 or WW2 naval battles. (Italian).
Mexican Revolution
Rules 25/28mm scale for the Mexican Revolution from 1910 - 1920.
Mexicanski
Spanish Civil War - rules variant of AK47.
Modder Fokkers
Rules for WWI air war. 1/72nd scale plastic models on stands made of wooden dowels on a 75mm hex grid.
Monte Carlo on the High Seas
Fast play rules for Battle of Tsushima Strait.
Naval War
Italian Language rules covering the period 1900 - 1960.
Naval Wargame Rules for the Russo-Japanese War
These rules are based on "De Bellis Navalis" by Colin Standish, published in Wargames Illustrated 143 August 1999.
Orrizonti Di Gloria
Italian Language WW1 rules.
Over The Lines
A set of aerial combat rules for use with 1/285 or 1/300 scale WWI aeroplane miniatures. The rules are intended to play quickly but accurately, hitting the sweet spot in the continuum between realism and playability.
Over There
Miniature rules for warfare 1900 to 1929. These are a scan of the original rules kindly provided by the author Nick Yankosky. They are designed for 15mm figures.
Quickfire
Pre Dreadnought era fastplay rules from The War Times Journal. (Beta)
Rabbidgerbal's Biplane Dogfight
Tighten your scarf and get your googles as you prepare to take on the Red Baron in this Rabbidgerbal's Biplane Dogfight in miniatures.
Red Actions
A game of company level battles and ambushes in the Russian Civil War Period.
Red and White
Russian Civil War, a fairly low level game, each unit probably represents a company. Additional rules for aircraft and ships available.
Red Army - White Guards
Figure game rules for the Russian Civil War by Graham Evans - originally designed for 15mm models and played on an offset square grid.
Red Hordes
A set of quick play Russian Civil War rules, similar to WRG's DBA/DBM and Hordes of the Things rules. Army lists are included.
Robs Naval Rules
A set of naval rules on 1 side of A4 for actions from 1890 to 1945. 
Russian Civil War 1918-1922
These rules are by Dave Waxtel and cover the RCW includes naming your army, army composition, political manoeuvring and tabletop rules. 
Russo-Japanese War
These rules are based on De Bellis Navalis by Colin Standish, published in Wargames Illustrated 143 August 1999.
Ten Rounds Rapid: White Heat of Change
Fastplay World War I rules (including organisations).
The Battle of Cambrai
A set of rules for using large numbers of tanks and infantry using squares on the table.
The Battle of Verdun
World War 1 Trench Assault rules in 1916.
The Breaking of Nations
This is a set of rules, written by Johh Bell, meant to emulate 25 mm skirmish actions during the Great War. It can also be used for an alternative or Sci-Fi vision of WWI.
The Price of Glory
Grand Tactical gaming of the Great War. Designed with 1/300 scale (6mm) figures in mind. (Recently Rescued). 
There's Something Wrong With Our Bloody Ships Today
These rules were written for the old Conquest Miniatures 1/5000 ww1 range. They are a very quick and Dirty set and have allowed us to fight "Jutland in an evening". 
Tierra Y Libertad
Fast-Play Wargame Rules For The Mexican Revolution, 1910-1920, in 25mm.
To Arms
Fastplay Card Driven Hex Based Interwar (WWI to WWII) Wargame Rules.
Togo
Rules for naval battles of the Russo-Japanese War of 1904-05.
Trench Assault
Simulation of the attack of a single Battalion across no-man's land in July 1916, demonstrating the problems of reaching the parapet before it can be effectively manned by the defenders. Suitable for any scale of figures from 1/300 to 25mm.
Trench Broom
Rules for 54mm figures for small-unit conflicts on the Western Front from 1916-1918. Join the yahoo group and rules are in the file section.
Tripoli: Blood & Sand
Fast-Play Wargame Rules - For The Italian-Turkish War, 1911-1912, and Sanusiyya Revolt, 1912-1931, in 6-15-20-25-28mm.
White General
Russian Civil War rules based on Ten Rounds Rapid: White Heat of Change.
World War 1 Rules
WWI Skirmish rules. They are free for download for individual use but copyright is retained by Mark Webb.
WW1 Aerial Combat
Hop into the cockpit and try to become an ace.
WWI Naval
For 1/3000th scale.
Zeppelin - Battles of the Great War
Set Piece battles WWI Variant Lighter-than-air Tactical combat.
Zeppelins Over London
The British players must attempt to shoot down as many zeppelins as they can before the airships move off the end of the board or time runs out.