When madwifi-project.org was launched (sometime in the Fall of 2005) we switched to a new codebase submitted by Atheros. This new code offers advanced features, including, but not limited to, a new HAL, support for virtual APs and WDS.
This driver is not fully open source, it requires a hardware abstraction layer closed source binary.
All PCI and Cardbus Devices with Chipset from Atheros
Enhanced Chipset Support
The HAL that comes along with the new code now supports almost all of chipsets that are currently available. There should be a new HAL soon which supports all of them except for USB chipsets.