nl80211 is the new 802.11 netlink interface public header. Together with cfg80211 it is intended to replace Wireless-Extensions. nl80211 and cfg80211 are still under development.
Users of nl80211
Current users of nl80211:
OpenWrt folks created a tiny version of libnl based on a git snapshot, which only contains genl, not rtnetlink or any of the netfilter stuff, and compiles down to less than 30k in binary size. You can find it here:
Kerneldoc for nl80211