  We celebrate the legacies of our friend and mentor Professor Lianshou Liu who
was one of the pioneers for the phenomenology of multi-particle interactions
and initiated the physics of relativistic heavy-ion collisions in China. In
this article, we discuss some of the recent exciting experimental observations
on the collective phenomena including collectivity, chirality, criticality,
strangeness production, and thermal equilibrium in high-energy nuclear
collisions. Future directions, especially the physics at high baryon density,
will be discussed with a focus on the first-order phase boundary and
hyperon-nucleon interactions.
