"Those on a tight budget or unfamiliar with WLAN analyzers may prefer to cut their teeth on shareware or open source programs. Depending upon your needs, you may even find these programs sufficient. We can't hope to provide an exhaustive list, but here are a few available shareware and open source programs to give you an idea of what's out there.
"Administrators that don't (yet) have officially-supported WLANs may find that shareware stumblers are useful for on-the-cheap rogue AP spot-checks..."