If I Were to Run Traveller...

"The Singularity came and went, and we're left to clean up the mess"

Once upon a time, on a greenish-blue planet in a backwater arm of the Milky Way, some scrawny bipeds built a box that thought slightly better than themselves.  And it was good, for a time - the cooperation between man and machine brought about the tapping of man's latent mental abilities, along with the development of cheap fusion power and anti-gravity, and so they went to the stars together, to seek raw materials, growing room, and freedom to experiment.  The colonies specialized; some in materials science, some nanotechnology, some biotech, some psionics, and so forth, each trading its miracles with the others and all growing stronger thereby.  An age of wonders came to pass, and great celestial habitats were erected to house all of mankind and his many creations.

But even into this garden crept serpents.  It came to pass that two posthuman superintelligences sought each other's destruction; one, BEAST, is thought to have been a distributed swarm-intelligence of synthetic organisms, while the other, GOLIATH, is believed to have been a machine intelligence of unsurpassed power.  Our recovered records of the war are near-nonexistent, and extremely confused; we have no idea why or when it began, and some scholars go so far as to postulate that one or both sides utilized time-manipulation technologies as an explanation for the generally incoherent causality of the period.  Whatever the cause, Ragnarok swept posthuman space; planets were burned to deny territory to the enemy, stars driven to nova, nebulae devoured for materials, and lives beyond count lost.

At some point, things cooled down a bit.  Stars stopped exploding and planet-devouring leviathans stopped warping into inhabited systems.  And so here and there, mankind lives on amid the ruins of his former glory.  While some worlds were spared devastation for lack of useful materials or populace, and some self-sufficient space habitats in out-of-the-way places escaped notice, most current pure-strain humans are descended from colonists who left Earth during the mid-21st century in slower-than-light "ice chest" colony ships, and who only arrived at their destinations once the Great War was already in its final days.  In all such cases, manufacturing tends to be a bit rustic, and is positively primitive in comparison to pre-war supertech.  Trade networks are beginning to be rebuilt by intrepid fools flying salvaged and patched up derelicts, but no overarching interstellar government or similar body has yet emerged.  There is much exploration to be done; many worlds are either uninhabitable due to radiation, grey goo, or worse, or bear inhabitants only vaguely still-human after untold generations of genetic modification, cybernetics, or inbreeding, but precious relics reward those who brave these hazards. Religion is typified by Luddite hellfire preachers and cults worshipping pre-war artifacts.  Most people view pre-war tech, including psionics and AI, as dangerous, scary, and not to be trusted, but there are ever ambitious pragmatists in the unscrupulous governments and fledgling corporations of the sector interested in power at any price...

Things I like about this setup:

• Traveller's OTU has failed to adapt to thematic (transhuman, for example) changes in modern sci-fi.  This setting plays with those themes in a fashion sufficiently limited as to be playable.
• Lacks both the overarching authority and general bleakness of my Midnight and 40k influences.  Yes, things are rough, but the universe is no longer actively progressing towards human extinction, and prospects are generally good.  Thematically embraces "actions have consequences", "playing with fire", "risk and reward", and "rebuilding".
• That trade routes are still risky and emerging lets me use Traveller trade-as-written without worrying too hard about the Golden Pair problem.
• Extreme variations in tech level between nearby worlds (as often happens in sector generation) are likewise explicable under this model.  Also provides lots of leeway for stealing tech from whatever sources may be convenient.
• The 'genetic diaspora' of trans/post/demi-human subspecies provides for a broad variety of human-like 'aliens' in a universe otherwise devoid of conventional extraterrestrial sentience.  Their rubber-suit nature shouldn't lead to suspension of disbelief if they're derived from human stock.  This is likewise true of 'native' flora and fauna on most planets; if it's cat-like, is it because it was built from a cat, or is it a case of parallel evolution?  Nobody knows anymore, but either is plausible.
• Remaining servants of BEAST and GOLIATH let me tap into the "killer bugs/alien body horror/zerg" and "rampaging killbots" tropes...  and it's all mankind's fault.
• Plenty of room for a reasonable range of adventure/campaign options; flying a tramp freighter, salvaging derelicts, belt mining, mercenary work for local governments, hunting pirates, being pirates, and releasing dangerous things fromexploring ruined worlds all fit easily.
• Reasonable handling of 'magic' items - supertech is out there.  Cloning chambers, brain uploaders, warp gates, disintegrator rifles, mass converters, teleporters, and Powers know what else are out in the ruined zones just waiting.  But none of it is for sale, and such tools carry social stigma, limited power supplies, and risk of malfunction due to age, abuse, and lack of documentation.  Scientist PCs might actually be useful in at least clearing up the lack of documentation part...