if you open some applications in kde and log out or shutdown your computer or device you can when log in again it automatically open the last open applications.
is that possible on unity 2d and 3d ?
Im afraid the ability to save sessions was dropped in Ubuntu 11.04 due to numerous side effects. There are currently no plans to re-enable it, which is a shame. Source.
There are three different general ways to accomplish something generally like this:
Firstly, suspend. This puts the computer into very lower power mode, but it isn't truely shut down. When you return from a suspend, everything is the same. NOTE: if power is totally lost, the state is also lost.
Secondly, hibernate. This takes the RAM and saves it to the swap space on the harddrive, enabling the computer to be fully shut down. When a computer is turned back on after a hibernate, the state is loaded back into RAM, and everything continues the way it was.
Thirdly, saved sessions. (FWIW, I suspect this is what you're referring to) This is when the desktop environment saves which programs are open upon log out so that when you log back in, it automatically starts up those programs. NOTE: the programs won't necessarily be in the same state they were before.
The answer depends on which of those you're wanting, and what version of ubuntu you're using.