They are grouped into two series: UNO and DUO:

UNO – a single group for coffee and steam.
DUO – a group for coffee and a group for steam.

Each series is divided into:
Fixed filter holder system (PF) for use only with ESE coffee pods
Mobile filter holder system for use with ground coffee and ESE coffee pods, simply changing the filters. Also FAP capsules, with an optional special filter holder.