"In the early 22nd century, a colony ship set out from Earth, bound for a nearby star system with a recently discovered Earth-like planet. When the Adventure arrived, the first crew-members out of suspended animation were quick to notice that, although the planet is approximately 25% larger than Earth, the gravity is within a few percentage points of Earth-normal. This mystery*, however, quickly took a backseat as catastrophe struck the vessel. A string of critical malfunctions caused the Adventure to begin sinking slowly towards the planet. Working quickly, the crew managed to bring it to more-or-less intact landing on the surface – but not before several chunks of the population had taken to the escape pods and rocketed off for parts unknown. Several generations later, a wide section of the continent upon which the Adventure landed has been mostly settled (centered on the crash site itself, which has become the location of the colonists' main city), and the Adventurers (for so the colonists call themselves) can afford some time from the business of surviving on this new world to searching for their lost kin."
Inspired in equal parts by the computer game Sid Meier's Alpha Centauri and this thread about superplanets on RPG.net, my idea for this was to create a backstory for some mix-and-match earth cultures, justified by the trauma inflicted on the escape pods' computers – who knows what historical and technological mishmash they were left with?
I do have a few ideas for these, (coming soon to a blog near you!) but there are huge possibilities for inserting whatever you like in there. Techwise, I'm imagining mostly modern to plausible near-future equiptment at the highest level - really good 3d printers, for example, or equipment to clone any necessary Terran animals - and at the lower end, again, whatever the escape-pod colonists managed to download into their computers before they took off- this could, if you wanted, lead to such anachronisms as, e.g. an otherwise Classically-inspired settlement arming its warriors with muskets.
And let's not forget, this is an alien planet they're on - even if they sent a terraformer ahead stocked with Terran plants and animals (and you just know some joker somewhere along the line smuggled recently-reconstructed dinosaur DNA into the clone banks), there's probably all kinds of weird native flora and fauna to contend with.
* The explanation for this is that the crust of this planet is riddled with natural** caverns and tunnels, causing the first mile or so of crust to be much less dense, overall, then Earth. Toss in some underground rivers, and you have a quick way to get from place to place, too.
** Or Are They?