Re: Most Powerful Sci-Fi Civilization
When they're on form, the Time Lords.
For starters they created the TARDIS, a virtually invulnerable ship that can travel through space and time, is bigger on the inside and is capable of hauling planets about (as much as I'd like to forget that ending).
And that's just the outdated "junk" the Doctor travels in.
They can teleport planets around time and space, trap them in eternal force fields or stick whole solar systems into a time loop at a flick of a switch.
The TARDIS (Tardii?) are naturally occuring spaceborn coral-like entities slaved to the Time Lords, bred for use as ships by inplanting technology (and carving out sections of their living interior) in their centuries long "childhood" phase when they still reside entirely in one dimension, growing to full adulthood about the size of Earth's moon.
"But there's no sense crying over every mistake. You just keep on trying till you run out of cake."