I have always wanted to build a fully-automated lawnmower robot. Main problem is prolly navigation tho. Best solution we had back in the days was some copper wire which marks the borders of the lawn and the robot working within that field with an induction coil on top of it. Problem was this went over my abilities back then. A week ago or so I have seen a Bosch device, the first automatic lawnmower I've seen so far for sale. It had no pricing so the price is surely big. It works with the same principle we postulated back then, I think the guy with the idea sold it to them.
Another invention would be the transistor that works with light. So the optical transistor. That would be revolutonary.
And another good invention would be all kinds of new propulsion, especially something spaceworthy. Maybe electrical engines that can utilize muons instead of electrons or other quantum physical things.
Last but not least, a nice product lifecycle chain would be nice. The "from cradle to cradle" concept so to say, in which a product lifetime and ressources are brought back into the cycle again.
For that we'ld need to reinvent tho society as a whole and make it less greedier and egoistic. That tho will never happen.