The Fast and Dirty science fiction rules have been updated to a fourth edition. The author writes:
F.A.D. is a skirmish rules set for science fiction and 20th century wargaming. The rules aim to provide a fun, fast and most importantly, realistic game.
Rather than troops charging blindly into gunfire, your men will be affected by suppression and losses. Officers are leaders and commanders, not supermen, and the emphasis of a battle is on men over materials.
During a battle, you will find troops getting pinned down and locked in bloody firefights, while trying to evacuate your casualties or bring up reinforcements to outflank that railgun position!
The game has its own background setting, but is generic and can be used with your existing miniatures and armies. The rules assume models to be mounted individually, but can work with any scale where this is practical. Typically this means 15mm and above.
The rules, as they stand now, cover infantry, artillery weapons, vehicles as well as peripheral scifi stuff like powered armour, drop troops and lots of other nonsense.
They will work for most 20th century and beyond games, with the emphasis being on modern day and near future warfare