They are grouped into three series: UNO, DUO and TRIO:

UNO – a single group for coffee and steam.
DUO – a group for coffee and a group for steam.
TRIO – two groups for coffee and one 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.