AD 2309 - Der Kampf ums Dasein (AD 2309 - The struggle for existance) is a German space opera setting. This version here is a stand-alone RPG, though a systemless version exists as well as an adaption to the German Liquid RPG rules. Here is a translation of the publisher's setting summary:
At the beginning of the year 2309, the Terran Union is in a dangerous situation: Its arch-enemy, the race of insectoid Tsrit, which threatens the existence of human civilization for about 140 years and could never be defeated, is seemingly gearing up for an annihilating strike against the Union. There is great uncertainty, however, because of their obviously open concentration of ships - a completely unusual tactic for this race.
But the Tsrit are not the only alien race to which humanity has established contact. There are colonies of the Lengroah in the human territories, a peaceful feline race that has lost its own empire in a war against the Tsrit and now supports humanity in the new conflict. The unfeeling reptilian Srakhs are the cause for many espionage incidents with their insatiable curiosity for information. And the ancient civilization of Arnesh, which - contrary to its own belief - has once saved mankind from their demise at the hands of Tsrit, but behaves strangely in the recent years. Making matters worse, there is also the message of a completely unknown race, who announced the destruction of many civilizations, among which they also count the human race...
But even within the Terran Union not all is sunshine and roses. Although it is officially a democracy, large parts of the decision-making power lies in the so-called Military Council. Many of the large interstellar corporations have a seat in this Council and with it power over the Union - and that power grows. Many companies don't care in the least about the social conditions in their colonies, and the theoretically guaranteed basic provisions trickle away on the way from Earth to the distant colonies. The rich colonies in the west of the Union fear for their existence or their prosperity and break openly with the Union. The interstellar space fleet as a fighting force of humanity has more tasks than just the protection of the Union against the Tsrit ...
AD 2309 uses d6, d10, d12 and d20.
An AD 2309 character is primarily defined by his six attributes (Strength, Dexterity, Endurance, Intuition, Mind, and Will) and his skills. Both are rated with positive or negative values that show the deviation from the human average. So a strength of 0 is the average strength, -5 would be a physically weak person, +5 would be a very strong character.
A normal human character (in contrast to a genetically engineered or android person) gets to roll 2d6 - 10 to determine the basic attributes and gets a certain amount of build points to increase the attributes.
Skills are bought from eight different build point pools. There is one pool attached to every attribute, and one physical and one mental point pool. Every pool has a certain amount of starting points that is modified by the attribute values. Every skill has a cost that must be paid from one or more of these pools.
There are two basic task resolution mechanisms: maneuvers and actions. A maneuver is a time-boxed task that may be fully completed, partially completed or not completed after the time runs out. Examples would be picking a lock or doing research on a topic. An action is a task that takes only a short time to complete and that either fails or succeeds, like jumping a chasm or firing a weapon.
For a maneuver roll the GM determines how much time the task would take for a person with an average skill. Then the player states in what time frame his character attempts the task. This modifies the maneuver value. The maneuver value is determined by the character's skill value and all modifiers that apply. The result is referenced on a maneuver table that shows if the maneuver took more or less time than expected, or if it failed completely.
The element of chance only come into play if the character is under stress. If the character has a higher stress level than normal, a stress modifier is subtracted from the maneuver value, but a die is also rolled and the result added to the maneuver value. The die size becomes bigger the higher the stress level is.
Maneuver example: A character wants to pick a lock. his skill level in lockpicking is +3. He has all the tools required and attempts his task in the average time. This would result in a maneuver value of +3, meaning that the lock is actually opened 0.7 times as fast as attempted. But the character is under high stress. That means that he must subtract -6 from the value, resulting in a -3. It also let's him roll a d12 to add to the value. And the stress table also says that a roll of 1 or 2 on d12 would be a fumble. The character rolls a 4 and succeeds with a final maneuver value of +1. This means he is successful and takes a tenth less of the attempted time.
An action has no time frame. The action value is determined like the maneuver value with the skill value as a basis, situational modifiers added or subtracted as the GM sees fit, and taking the stress level into account. Any resulting action value of 0 or higher is a success.
Combat uses a modified skill mechanic. The attacker determines the kind of attack and the hit location he wants to hit. He then rolls a d20, adds his skill value, subtracts 10 if the defender is fully aware of the attack, subtracts the defenders dodge skill, and applies all situational modifiers. A result of 0 or more is a successful attack on the intended hit location. If the result is less, the attack may hit another hit location. The direction in which the attack deviates is determined by a d12 roll. Then a d20 roll is multiplied by the weapon's deviation modifier. The resulting number shows how many centimeters the hit deviates in the given direction. The GM determines if the target is hit at all and where. Damage is subtracted from different status values (blood, structure).