How are these different from HRV - Heat recovery ventilation?

HRV's exchange only heat. ERV's (where E stands for energy or enthalpy) also exchange moisture. One is not strictly bette than the other, it depends on your house and your climate: https://www.greenbuildingadvisor.com/article/hrv-or-erv

These require a ducting system, correct?

Not necessarily. There're units that are installed in, basically, hole in the wall.

This makes them very attractive for older renovated building, which used to rely on drafts for air circulation.

There was a link in the comments on this site awhile back from a company that made on similar to an AC window unit, and it had an optional active HEPA filter add-on, whick looked similair to a portable ducted AC.

Also, Panasonic makes a bathroom fan ERV for about $400, which you can find on Amazon, with two ducts, one for fresh air intake, and the other to vent the stale air, and you need to have the intake and exhaust ideally on opposite sides of the structure.

Some people use it for their basement humidity levels. It is much less expensive to run than a dehumidifier.