Event Horizon is a set of free wargames rules for quick play starship combat. It is played on a grid board.
Rules: Science Fiction
Inquisitor Rules 40k Universe
Inquisitor was game produced by Games Workshop set in the Warhammer 40K Universe. Curiously, it used 54mm figures.
The game is out of print, but a rules archive is at the link.
Fires of Space Rules
Fires of Space is a space combat game with a WWII naval flavor. From the author’s introduction:
Here is my take on battles between big ships in space. This rules set has a deliberately 20th century naval warfare flavor, but with adaptations for space and far future technology. Included are the rules, tables, designer’s notes, a series of ships from various space navies, scenarios, a probability table for 20 sided dice, counters, and a 50 by 50 hex map. With the map are marked map sections showing showing the map’s center hex and deployment areas for tactical scenarios. Ideally, the game is played with two 50 by 50 hex maps: one for operational movement and the other for tactical engagements. In a pinch, a single map can double as both the operational and tactical map. Finally, I include a copy of the Excel workbook that I used to create the ships in the game.
Combat Squad Warhammer 40 K Skirmish Rules
Combat Squads is a set of home rules for gaming in the Warhammer 40K Universe. From the rulebook:
Combat Squads is an attempt at creating a set of competitive skirmish rules for Warhammer 40.000; a game set in the grim darkness of the far future.
Within this booklet you’ll find rules for constructing, and playing, with small Combat Squads using the miniatures you already have for your regular Warhammer 40.000 army.
As such, then you’ll need the core rulebook for Warhammer 40.000 (currently, the 5th edition rules) in order to play Combat Squads. Furthermore you’ll need this booklet, of course, and the codex for your chosen army.
The rules presented here in the following are intended to supplement your normal games of Warhammer 40.000 giving you a chance to play the odd one-off special mission during a campaign game. However, they have also been
written in such a fashion that you could play Combat Squads as is; with an inbuilt campaign system as well as a slew of new missions.