MadWifi is a Linux driver for IEEE 802.11 Wireless LAN devices that are based on chipsets from Atheros. It supports all relevant modes of operation (client, Access Point, 802.11 IBSS aka ad-hoc, ahdemo, WDS, monitor), state-of-the-art encryption (WPA, WPA2, 802.1x), Multi-SSID operation, and more.
Older versions of the driver depend on a binary Hardware Abstraction Layer (HAL). Meanwhile, the source for the HAL has been released under a permissive license and is now included in the MadWifi source.
Development of MadWifi has more or less ceased, the driver is superseded by ath5k and ath9k (which are part of the Linux kernel).