OpenBSD's hostapd is a user space daemon that helps to improve roaming and monitoring of OpenBSD-based wireless networks. It implements Inter Access Point Protocol (IAPP) for exchanging station association information between access points. It can trigger a set of actions like frame injection or logging when receiving specified IEEE 802.11 frames.
The Open Wireless Linux version of hostapd. It is kept as close as possible to the original open source release, but with OWL specific packaging and defaults. The Website appears to be dead (April 2013), probably as the project itself.