I'd recommend you to use the Mongoose Traveller rules, which are quite good, flexible and rules-light yet very adaptable to almost any sci-fi scenario you have in mind. Simply ignore most of the Official Traveller Universe (OTU) which is a Dune-esque/Foundation-esque Humano-centric universe with a 1960's sci-fi feel to it and simply build your own setting, which is quite an easy and enjoyable thing to do with the Mongoose Traveller rules.
Sure, Traveller jumps take a week each, but if you keep the tech-level low (which, it seems, what you already intend to do), that will be a week per 1-2 parsecs; a moderately-sized setting (sector or so - circa 40 parsecs across) would be
months of travel away from the core. Then, if you use the optional 'hard science' world generation rules in the Mongoose edition, most worlds would be rockballs with low populations; major habitable worlds will be months of jump-travel away from each other, with various low-population, scantly-explored, Acheron-like worlds in between.
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More about Traveller - an edited repost from
an old thread:
Traveller comes in many editions, and its rules and assumptions vary between them. The following will be most relevant to
Classic Traveller (CT) and
Mongoose Traveller (MGT), both being relatively popular versions. Mega Traveller (MT) and Marc Miller's Traveller/Traveller 4th Edition (T4) are also similar in many aspects but different in others. There are also Traveller: New Era (TNE) using a variant the Twilight:2000 rules, Traveller D20 (T20), GURPS: Traveller and Traveller Hero; these versions differ in many ways from CT, MT, T4 and MGT.
So let's get into Traveller itself. Traveller (originally published in 1977) was originally designed to be a generic sci-fi ruleset compatible with a wide array of sci-fi settings, especially of the 1960's-1970's interstellar kind. All editions of Traveller come with many world-building rules - random world generation, ship-design systems, and in some cases alien critter ("animal") generation systems and vehicle design systems. It is entirely possible - even desirable - to build your own setting for Traveller and ignore any official setting material - in fact, the original rules has no official setting at all!
Traveller has long been associated with the Official Traveller Universe (OTU), an Asimov-style (so I've been told) space-opera affair centered on the Third Imperium. But you can easily ignore the OTU and go with your own setting.
The basic Traveller game mechanic is roll 2d6+skill level+modifiers; a roll of 8 or more is a success. Skills usually range between 0 and 3 but could be higher; characteristics (ability scores) usually range from 2-12, with 1 or 13-15 in extreme cases. Classic Traveller has several varieties of this mechanics for different uses, but MegaTraveller and Mongoose Traveller use a coherent "task system" with coherent characteristic (ability) modifiers. Difficulty is also a die modifier in most versions.
Traveller is skill-based. At their heart, characters have six characteristics (Strength, Endurance, Dexterity, Intelligence, Education and Social Standing) and a number of skills. In Classic Traveller, your entire "character sheet" (other than gear, money and ships, of course) could be summarized in a single short paragraph! There is a wide range of skills, from Admin (a social skill used to deal with bureaucracies) through things such as Gun Combat (several skills, depending on which kind of guns you want to use) and Pilot (used for piloting starships) to Medic and Vehicle skills. At its core, Classic Traveller had 27 skills; later versions have more diverse skills.
Character creation is semi-random and based on resolving the character's pre-adventuring career. Traveller characters start the game as experienced adults rather than 18-years-old beginners. Most character development (in the game-mechanics sense) takes place during character generation; during play, most character development is in terms of knowledge, personality, possessions and political power, while acquiring new skills is a very slow process. But that's OK, since you could start the game as a very experienced professional!
Traveller technology mostly has a "hard science" feel to it. Sure, there are anti-gravity vehicles, reactionless drives, psionics and jump (read: slow FTL) drives, but other for these the technology seems very plausible and even "conservative" (AIs are rare and there is almost no nano-tech to speak of). The majority of ground weapons are slug-throwing guns, with energy weapons typically being heavy support weapons.
A basic concept of Traveller is that communications are limited to the speed of travel - there are no "hyperwave" or "subspace", so the fastest way you could communicate is by courier ships, and these at best could cross 6 parsecs (about 19 light-years) in a week-long Jump, and that's with the highest possible tech-level. Most ships - in fact, all ships for lower-tech settings - are far slower, a week-long Jump for them cross less parsecs (a parsec is approximately 3.26 light-years). Due to this communication lag, large interstellar governments have to be fairly decentralized - as asking for specific orders would take week, months, or even years. This is a good thing for the game as it means that PCs in a frontier area are on their own, with the major authority figures tucked away a few weeks (at most) of jumps away.
As I've mentioned in my previous post, Traveller has a comprehensive random system for generating worlds. Each world has eight characteristics - Starport (how good the port facilities are), Size (how large/heavy is the world), Atmosphere (what atmosphere it has - some kinds are breathable, others are not), Hydrographics (which percent of the world is covered with water or other fluids), Population (how many people are there), Government (general class of government - e.g. Representative Democracy, Impersonal Bureaucracy, Charismatic Dictatorship and so on), Law Level (how restrictive the world's law enforcement system is, especially in regard to guns) and Tech Level (how advanced is the local technology, ranging from "0" for stone-age to "15" or "16" for sci-fi high-tech). Generating worlds in Classic or Mongoose Traveller is fast once you're experienced with it - I've recently generated a whole subsector (see below) of around 30 worlds in about 2-3 hours.
As an abstraction, Traveller uses 2D space maps (rather than realistic 3D). It isn't very realistic but its very comfortable to work with. The game divides space into hex-grid "subsectors" of 8 parsecs by 10 parsecs (neatly fitting unto an A4 page). Four subsectors are a quadrant; four quadrants (or sixteen subsectors) are a sector; and four sectors are a domain (in the official universe's Imperium, and Archduke rules a domain). Most campaigns could be played in a single subsector or quadrant, or, at most, a sector.
Combat is fast, rules-light (yet, in Mongoose Traveller, covering a surprisingly wide range of possibilities for its mere 9 pages) and deadly. Very deadly. While a typical character has a good chance of surviving a gun shot, each shot is very damaging and two or three shots (or even one in some occasions) would kill each character. Combat uses the same basic "2d6+skill+modifiers for 8 or more" mechanic as any other skill roll; things such as range or cover modify that roll. Damage is subtracted directly from the target's physical characteristics; when two are reduced to zero, the character becomes seriously wounded and unconscious; when all three are zeroed the character is killed. Vehicle and ship combat is similar and quite rules-light but uses hit-location tables (listing things such as weapons, drives, passengers, fuel etc).
