K9 was the designation given to a series of intelligent, dog-like robots who served as companions to Professor Marius, the Fourth Doctor, Leela, Romana, Sarah Jane Smith, Luke Smith, and Starkey. K9 Mark I, II, III, and IV addressed whomever is directing them as "Master" or "Mistress" depending upon gender, and used the formal "affirmative" and "negative" rather than "yes" and "no". They were programmed to be both loyal and logical, with a penchant for taking orders literally, almost to a fault.
We like tracking our technology round these parts. Only problem is that the show is about a time travelling scientist. And he's spawned shows like Torchwood that are entirely focussed on alien tech. So there's a lot of tech sittin' around the joint. Be bold, though, and start your journey at category:technology.
When looking for a piece of technology on this wiki, it's helpful to think about some of the broader categories. Looking for the tech of a certain species? Go to technology by species.
The DWU likes its sonic tech, doesn't it? But it's not just the sonic screwdriver you have to keep an ear out for. Don't forget, the Ice Warriors and several other species are heavily invested in sonic technology, which you can find at category:sonic devices.
One of the broadest classifications of technology is communications technology. Since the series is about a guy who likes to talk a lot, we figure that only makes sense!