Given that the lifetime of current storage media is less than 100 years and the possibility of planetary devastation is non-zero (by asteroid impact, nuclear war, global warming, creationism, etc), today’s invention is a way to perform an ongoing off-site backup for all our digital information.
I envisage mooring a transmitter/receiver at the Earth’s L2 Lagrangian point (reasonably well protected from earth-centric disasters and it makes the geometry simple for a long, long time).
I’d also have a small reflector craft orbit the Sun (way outside Earth’s orbit).
We beam all our important information via radio to a receiving dish at L2 which resends it to the reflector craft and back to L2 in a continuous loop (pausing only when the Sun gets in the way).
Electromagnetic signals in vacuo are not attenuated (if you avoid solar flares and pulsars and ignore the inverse-square law effects) so placing all our data in space transit is a way to ensure that almost no bits are lost. 1bit for say 10 wavelengths would eventually allow an enormous amount of knowledge to be accommodated by this virtual tape loop.