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 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:
CoovaAP is another firmware replacement, based off of OpenWRT, specifically designed for Wi-Fi hotspots. It has the CoovaChilli access controller built-in, giving you captive portal, access provisioning, and accounting features. You can require hotspot users to login with accounts (self registered or defined by you) or just require users to agree to the Terms of Service (ToS).
CoovaAP also sports WDS (wireless distribution system), great if you're setting up multiple APs. If you or your organization has a Facebook page, you might want to check out the Facebook captive portal feature. The firmware also has traffic shaping controls so you can limit the bandwidth your guests use.
Open-Mesh is perfect for larger hotspots requiring two or more APs, or even when covering an entire apartment complex or campus. The open source firmware provides the brains and gives you a zero-config, plug & play, and self-healing wireless mesh network. Plug a Open-Mesh node into the Internet and place other nodes nearby to repeat the wireless signal without running Ethernet cables to each. Then you can use their free Dashboard to remotely control and monitor your nodes and networks.
Though you can flash your own supported equipment with the Open-Mesh firmware, you'll probably want to buy their branded gear right from their site. The lower-cost model starts at $29 and the professional model with Power-over-Ethernet (PoE) and a few other enhancements goes for $59 each.
Both Open-Mesh nodes offer two ESSIDs (network names): one for the hotspot users and a separate one that can be encrypted for secure private-use. You'll also find captive portal features, user authentication and billing options via third-party solutions from Coova.org, WiFi-CPA.com, WorldSpot.net, or your RADIUS server. You can impose bandwidth limits on the public side.
I've also done a tutorial series on Open-Mesh, check it out for more details or for help on getting it setup.
The ZoneCD solution is not a firmware project like many other solutions here. It is a LiveCD loaded with Linux software, preconfigured to serve as a hotspot gateway. Insert the CD into an old computer with two network cards and you have yourself hotspot user authentication and web content filtering. A GUI is provided so you don't even have to know anything about Linux.
The hotspot gateway is configurable through a web-based control panel. The free service gives you the basic hotspot functionality. Premium services let you have more control over users and the hotspot, and gives you better support.
FON isn't a mundane hotspot solution. They even have their own language. Fonera is what they call their line of branded Wi-Fi routers. When you share your wireless Internet, creating a FON Spot, you're called a Fonero. Then you can opt-in as as a Bill to receive 50% of the net revenues, or remain a Linus if you don't want free money. You'll also be able to use other FON Spots for free, unlike Aliens which aren't sharing and must pay or view advertisements to use FON Spots.
FON's newest wireless router, called FONERA 2.0N, at $99 provides many more features than the original La Fonera and La Fonera+. Its USB port opens up a whole new world. You can go mobile by plugging in a 3G adapter, download torrents with your PC shut off, quickly upload Videos to YouTube, easily upload your photos to Picasa, Facebook, or Flickr. You might even connect a drive use to use it as a central storage spot (NAS) for all your PCs and Devices. The FONERA 2.0N can even Tweet on Twitter, for example, to let you track downloads and user connections.
RouterOS isn't just for hotspots, its a complete Linux-based network and routing operating system. Thus this solution isn't for beginners, it requires more knowledge on network administration. You can, however, download and install RouterOS right onto regular PCs. Just make sure you have some sort of storage drive (IDE, SATA, USB, SD, etc.) and you'll probably need at least two ethernet cards.
The hotspot features of RouterOS include a captive portal, internal user directory, user accounting, and bypass for non-interactive devices. It even has trial user and advertisement modes. For more info or configuration help, you can visit their Wiki and documentation.
Eric Geier is a freelance tech writer. He's authored many networking and computing books for brands like For Dummies and Cisco Press. He is also the Founder and CEO of NoWiresSecurity, which helps businesses easily protect their Wi-Fi networks with the Enterprise mode of WPA/WPA2 encryption.