This type of units can act with your visitors directly. Instead of clicking they also can be contacted by the Inviter / Greeter itself. The greeter is able to welcome the visitors to your region or closeby and send out a Hello, while the inviter can send a group invite. Those units can also react on being clicked instead if needed. So they are like Infoboards with the possibility to invite / greet without any clicks.
These units can work stand alone or with a standard server (not with a tiny server) like ST100 or SX101.