In its most basic explanation the:
Web card delivers SNMP, Telnet and web management capability for a UPS or cooling system.
Relay card provides contact closures for remote monitoring of alarm conditions.
More detailed information from the Liebert website is below.
Liebert IntelliSlot Web Card family delivers SNMP, Telnet and web-management capability for enhanced communications and control of Liebert UPS, power management or precision cooling systems. Effective data center monitoring is provided by a wide range of operating parameters, alarms and notifications; transmitting data over the network.
The interface provides for remote web or in-the-field firmware upgrade. Alarms and parameters are transmitted over the network using SNMP, email, and SMS text. In addition, Liebert IntelliSlot Web Card w/Adapter supports Modbus.
Liebert Intellislot Relay Interface Card provides contact closures for remote monitoring of alarm conditions of Liebert UPS systems equipped with an Intellislot communication port. Proactive data center monitoring is provided by On Battery, On Bypass, Low Battery, Summary Alarm, UPS Fault and On UPS signals to relay contact monitoring systems. The card is user-installable and hot-swappable.