Oracles are an essential part of solo roleplaying.
They fill in the role of GM to a large extent, throwing up additions to the evolving story as we probe and ask questions of the world and the events within.
There are a few well-known oracles that take up whole books, filled with tables and outcomes, but what I want to promote here is a very easy to use, and fast, oracle which is not only versatile, but also completely free.
It involves a simple D6.