The AVM NDIS WAN CAPI Driver is a driver that typically supports AVM hardware devices (such as FRITZ!Box or other AVM communication products), enabling them to interface with network protocols using NDIS (Network Driver Interface Specification) over a WAN (Wide Area Network) connection. CAPI stands for Common ISDN Application Programming Interface, which is a standard for communication with ISDN (Integrated Services Digital Network) devices. This driver allows Windows to communicate with AVM's ISDN hardware devices, which may include the ability to connect to the internet or provide voice services through ISDN lines.