Many countries have higher degrees than the PhD.
In the UK, there's
- Litt.D Doctor of Letters / Literature
- DSc Doctor of Science
- LL.d Doctor of Laws
- D.D. Doctor of Divinity
Each of these typically requires the submission of a body of work - a research portfolio - together with a critique of the work. Or they may be awarded as honorary degrees; see the links above for the requirements for the degrees from the University of East Anglia (Litt.D, DSc, LL.d), and the University of Oxford (D.D.), accordingly.
A post-doc is just an academic research job that's typically done after attaining a PhD. It's not a degree in its own right