Created by Dave Morris and Jamie Thompson, these were an interesting concept. For those who never encountered this series, it was supposed to consist of 12 linked books that allowed you to travel from one to the other at will.

It's effectively a giant sand box - in book format. Certain points would earn (or lose) you a code-word (list in the back with stats sheets), which had a variety of effects from increasing profits/losses to preventing certain encounters from being repeated.

Sadly, the original run fizzled out around the 6th book, and it was never fully released, although a crowd funded reprint campaign was successful in making a fresh attempt.

The books are still available from Amazon at the original price. The have also been formed into a java app, available here: http://flapp.sourceforge.net/