You'll find many Linux-based and/or open source options when searching for a Wi-Fi hotspot solution. Whether you're wanting to give away or charge your visitors for the wireless Internet, you should find something that will work. The best part is that most of these solutions are free -- you don't have to spends hundreds on a off-the-shelf hotspot gateway.

DD-WRT

DD-WRT is a firmware replacement you upload onto a supported wireless router. This changes your router's control panel and gives you many more features, including several hotspot solutions: Chillispot, NoCatSplash, WiFiDog, and Sputnik. You might also find a use for the other new features as well. For example, you could create a separate wired or wireless network for your private network with VLANs and multiple SSIDs.

Here's an overview of the hotspot features in DD-WRT:

• Chillispot: Gives you great hotspot authentication and management features for free or commercial hotspot locations, but requires an external RADIUS server. However, you can use hosted servers from companies such as Worldspot.net, HotSpotSystem.com, and WirelessOrbit.
• NoCatSplash: Provides a quick and simple captive portal, but doesn't include user login or management features. This is still great for single hotspot locations where you want users to agree to Terms of Service (ToS) before getting access.
• WiFiDog: Gives you an advanced captive portal and content management for free hotspot locations. However, you must configure a proprietary external server.
• Sputnik: Provides free and commercial hosted services that gives you user authentication and device management for use with free or pay access hotspot solutions.