Economically viable enters into it as well. Just some guesses though:
1) Cars that drive themselves
2) Space Elevator
3) Quantum effect transistors (ultra-small switches at the limit of Si manufacturing. I'll bet real money on this one happening.)
4) Quantum computers (Not the ultra-amazing computers that some people think, but they will be able to make P=NP, which will be a huge improvement.)
5) Huge advances in medical technology resulting in lifespans typically around 100 years for people born at that time.
Well heck, my grandfather, born in the 1890s, was 99+ when he passed away. My mom is his youngest and is 78.