5. Babel Fish
"You'll need to have this fish in your ear."
"I beg your pardon?" asked Arthur.
Just how exactly is an intergalactic traveller supposed to get along with an incomprehensible number of languages out there? You can't very well just set about learning how to order a Pan Galactic Gargle Blaster in over 1,000,000 languages. Well this is where the Babel Fish comes in; it is "small, yellow, leech-like, and probably the oddest thing in the universe" and is capable of translating any language into any other language when inserted into the ear.
Thanks to the likes of Google and Skype, this is fast becoming a reality. We've been able to translate text for a while now, but what about speech? Well, Skype have unveiled their prototype software that will translate audio from one language to another in real time, allowing you to videochat with somebody in two completely different languages, without the embarrassing possibility that your GCSE Spanish might fail you at any moment and leave them flummoxed when you cheerily enquire where they have parked their dead goat.