Your very own diary or journal, which "tells on" everything, happening within you, happening without you! (See Multidimensional Language)

Also:

The Tao Te Ching (How things work...in the universe!)

I Ching ("e-ching" - Book of Changes...How sameness and consistency co-exist with change. Order with Chaos!)

The Bhagavad Gita (Finding a lost friend, discovering a universe of undaunted truth!)

These books, (all 4 of them! ), thousands of years old, as relevant now as when written, are taught in universities all around the world.