Mothership

Characters in Mothership must pick one of four classes, all of which should be very familiar to fans of Alien and similar movies: Teamster, Scientist, Android and Marine.  Like many RPGs, characters also have core statistics, but the game keeps things simple with only four such stats: Strength, Speed, Intellect, and Combat.

Characters can also skills, which add a bonus to the relevant statistic when making a roll that uses that skill.  Speaking of rolls, Mothership uses a d10 based system, but it has a unique convention of differentiating between d10 rolls that go from 1-10, and underlined "d10" rolls, which instead treat the d10 as a percentile dice (eg. 2d10 would generate 20-200).

In addition to creating their individual characters, the group an also create their own custom space ship.  As you can see from the ship's "character sheet", there is plenty of detail to this process, allowing for each group's ship to be unique.

To accomplish most things in Mothership you make stat checks, similar to skill checks in other systems (since having the relevant skill adds to your chance of success).

To make a stat check, the player simply has to roll less than than the appropriate stat on 2d10.  If you roll the same number on both d10's, the check becomes a "critical", either a critical success if it would have succeeded, or a critical failure if it wouldn't.

Like (modern) Dungeons and Dragons, Mothership also has the concept of "advantage" (when circumstances make a check either) or "disadvantage", which lets the player make two rolls, and then lets/forces them to keep the highest/lowest.  Similarly it also has the concept of saving throws, which you make to avoid suffering ill effects.  There are four saves (Sanity, Fear, Body, and Armor) and, like a stat check, you have to roll under the appropriate one to successfully save.

Owing to its horror nature, combat in Mothership begins with the players making a Fear save simply to be able to act.  After that initiative is determined.  All enemies in Mothership act together, so initiative involves making a Speed check to see if you go before or after the your foes.  Characters with certain skills, Commander and Tactician, get a bonus to initiative, which they can share with others.

On each round of combat a player can take two actions, such as attack, bandage an ally, or move.  To attack the player makes a check using the appropriate stat (possibly with bonuses, eg. from skills), and the defender makes an Armor save.  If  the attacker rolls higher than the defender, without the defender rolling over their Armor save, the attack hits.

As a horror RPG, Mothership also has another form of "mental damage", known as stress, and rules for panicking when faced with alien monsters.  However, as a space RPG, it makes sure to include a full set of rules for handling ship-to-ship combat as well.