A good product shouldn't require a training manual or even that much text to be initially useful to a user.
The trick is to have clean and clear UI/UX metaphors that seem obvious, great "clean slate" experiences that nudge the user to do key things when they first log in and in-line tips for what to do next (just 1 or 2 sentences at most). In this way, users learn how to use the software organically.
Tips, tricks, help and knowledge base should only be available for some advanced functions or to handle edge cases.
What are some of the best examples of this you've seen in the wild?