Basically anything the plot of a particular episode requires. The only thing it can't do is work with certain types of deadbolt locks. Otherwise it's been used for everything from unlocking doors to attacking Daleks. It also has a computer inside capable of making complex calculations requiring centuries to complete, and "The Day of the Doctor" confirms it has some sort of "cloud" aspect as it's able to transfer calculations between different screwdrivers over time. One thing rarely if ever done with it, though, it actually unscrewing screws. "Shroud of Sorrow" (BBC New Series Adventures novel), an Eleventh Doctor novel published in 2013, has the Doctor using it to remove screws and suggests this is the very first time he's ever used the screwdriver for doing that.