WHAT IS IT?
A quipu is a recording device which is made from thread and knotted in a significant way or place. They come to us from South America and were developed by the Incans but, due to the Spanish invasion the practise eventually died out 
WHERE DO YOU GET IT?
A few museums will have an exhibit of quipu but if you were striving for authenticity then you could probably save time and a considerable amount of legal fees by making one yourself. It will do you no good to learn Incan however as the incredibly intelligent people  who study these knots haven't yet found a link between the quipus and Quechua, which was the native language of the Peruvian Andes
USING IT IN REAL LIFE:
If/When the alien hordes stop watching television and finally invade us then there will certainly be some kind of resistance that quickly gets set up  A quipu would be a cheap and incredibly secret way of sending messages.
If you keep homing pigeons then you might consider a quipu rather than a tiny slip of paper. You'll be able to encode alot more information onto the string and the pigeon will be able to use it in her nest afterwards. Everyone wins!
USING IT IN WRITING:
Well I've already beaten you to it this time!  I was looking at a method of writing to be used in Harts Change and the quipu was mentioned in an article of Egyptian Hieroglyphia. Intrigued I started reading more about it and decided to steal the concept for the book.
So how might it be used?
- Passing secret messages back and forth as noted above.
- As an alternative to paper. 
- Perhaps authors are venerated in your writings. Wearing your quipu might be a status symbol.
- It may be that each person has secret knots which ensures that they are the only ones who know exactly what the book says. What would happen if someone discovered the secret or developed the same knotting?
Another Q word that I came across while looking up quipu is QUED. This is an old english word that means bad or evil.
It caught my attention because QUOD ERAT DEMOMSTANDUM is a Latin phrase meaning 'which was to be demonstrated' and, this is the important bit, as QED.
Just thought I'd include it in todays posting because someone out there might be saying "Hey! I can do something with this" 
MIGHT ONE TAKE OVER THE WORLD WITH IT?