deborphan - apt-get autoremove
 

man deborphan:
deborphan finds packages that have no packages depending on them. The default operation is to search only within the libs and oldlibs sec‐tions to hunt down unused libraries.

man apt-get autoremove
apt-get autoremove (--purge) is used to remove packages that were automatically installed to satisfy dependencies for other packages and are now no longer needed.

so what actually is the differce? (btw apt-get autoremove always lists much more packages as deborphan)

The difference is unless you know exactly what you are doing autoremove can break your system.

Autoremove will look at your package list and see groups of packages that have been installed by metapackages. If you have removed a package that was install by a metapackage that metapackage would also have been removed leaving a list of other packages that were also installed by the metapackage that can apaprently be removed. Problem here is you may actualy want them and there can be a lot of them. An example of this is ubuntu-desktop, which is a metapackage, in Ubuntu. If you have a preference for say VLC instead of Totem and you remove Totem because you no longer want it you will also remove ubuntu-desktop. By removing ubuntu-desktop you have now made the majority of the Ubuntu system available for autoremove.

Deborphan on the other hand doesn't check in the same way. It only checks what packages are actually required by other packages. If you have removed a package and that has left a couple of packages "orphaned" or not able to be used because the reason they were there is now gone (which is very different to a metapackage scenario) then it will list them.

Hope that helps.