I'm trying to find some finite temperature properties using ab-initio simulations; and for this, I'm looking for a tool to be used as an auxiliary to DFT simulations (in VASP) to implement Quasiharmonic approximation (QHA). I'm facing some problems using Phonopy, so, could anyone tell me what's a popular package for QHA?
To answer your question, the most popular right now is phonopy. If you are having a technical problem you can post it on GitHub, usage issues are better suited for the mailing list. My opinion is that, if possible, using phonopy and getting it working would probably be best for the community if it is a technical problem in the code or best for you if it's just a usage issue.
If you must use another software, YPHON was developed in my research group and the same formalism is used by phonopy and is cited as such.
Quantum-Espresso has some QHA tools I believe. And many of the equations are pretty simple, if you are up to coding some of them yourself. See this useful paper.