Traveller

Like many "old school" role-playing games, character creation in Traveller is very random. You begin by randomly determining your six stats, using 2d6 for each: Strength (STR) , Dexterity (DEX), Endurance (END), Intellect (INT), Education (EDU), Social Standing (SOC). Those first four are analogous to Dungeons and Dragons attributes, while Education and Social Standing are unique to Traveller.

But the randomness doesn't stop there: after rolling stats you do get to choose a few skills, but then you're on to an entire "mini-game" to determine your character's career path. During this mini-game your character starts at age 18, and then you get to choose their path through life via four-year increments.  In previous editions, you could even die during this min-game!

In each four-year increment you can try to pursue one of twelve various career paths (Army, Entertainer, Merchant, etc.).  Also, early on your character can choose to instead pursue an educational path (eg. university or military academy), and if things go poorly later in the mini-game there's a thirteenth "career path" of prisoner.  However, to succeed at any of those paths you need to successfully make a random roll (eg. to be a scientist you need to make an Intelligence check).

Each career offers either tangible benefits (eg. money, weapons, shares in a spaceship) or non-tangible ones (eg. combat implements, characteristic improvements).  If you stay with most careers for at least five rounds (ie. twenty game years), you can even qualify for a pension, giving you money that you can collect each year.  However, once a character reaches age 35 they start making aging checks, which can result in lowered stats.  You can avoid the checks by using anti-aging drugs, but those are both expensive and illegal (potentially resulting in the "prisoner career").

After the min-game is done your character is ready, but you still need to connect to the rest of the group, by "writing your character in" to the major life events of up to two of their fellow characters (those events occur as part of the mini-game). Doing this  gives both characters a point in a related skill.  Finally, the group selects a skill package (eg. Starship, Explorer, Mercenary), which provides skills to the entire group.

Although human is the default race, alien races are an option in Traveller, and the core book offers two such races as starting options (the feline Aslan and the canine Vargr).

To determine whether your character in Traveller succeeds at an action you make a skill check, by rolling 2d6 and adding tour character's skill level and relevant characteristic modifier (plus any other applicable modifiers).  If the character isn't trained in the skill they get a -3 penalty, and a roll of eight or greater succeeds for an average difficulty task (though the GM can adjust that number for easier/more difficult tasks).

If the degree of success is important, the "Effect" is determined by subtracting the difficulty from the number rolled (eg. rolling a 9 for an average difficulty task would result in an Effect of 1). The amount of time spent on an action can also impact it's success (ie. spending more time than normal can lower the difficulty, while spending less raises it).  Also, to simulate easier/more difficult circumstances the GM can assign "boons" or "banes", which add an extra die (with the player taking either the higher or lower roll of the two dice).

Traveller also has "Task Chains", where the results of one skill test influences other tests that follow (for instance, if you perform a Recon action, it's success may impact the success of your subsequent Stealth test to sneak into an enemy stronghold).

In Traveller Combat is divided into rounds, with initiative established once at the start of combat.  In each round a character gets a significant action (eg. attacking), a minor action (eg. drawing a weapon, moving), and a number of reactions and free actions.

To attack in Traveller you make a skill check, using the appropriate skill (eg. melee or shooting), and adding the appropriate stat to a 2d6 roll.  The target can then react, eg. by dodging (which gives the attack a penalty of their Dex or Athletics skill).

In Traveller there are no "hit points"; instead damage is applied first to the targets Endurance stat, then to either their Strength or Dexterity.  If either of those latter stats drop to zero, the character goes unconscious (and risks dying).

Because even a basic pistol does 3d6 damage, and stats don't increase with levels (the way hit points do, in other systems), unarmored combat in Traveller can be extremely lethal, with a character dying after taking only a couple of hits.