Plenty of WiFi routers have guest modes for visitors; some companies base their entire business models around them. Many of these devices are full of security holes, however, and the Electronic Frontier Foundation doesn't see that as acceptable in an era where widespread government surveillance is a fact of life. To fix this, it has posted a very early version of custom-built open router firmware that promises both easy access and security. While there is a guest mode, the new firmware (based on the existing CenoWRT) should patch common exploits that leave your home network vulnerable. It will even fetch signatures for updates through the anonymizing Tor network to prevent rogue code from posing as a necessary upgrade.
It's not all about locking down your access point -- there are some conveniences, too. You can limit the bandwidth guests use so that they don't kill your own connection, and there's "state-of-the-art" network queuing to make sure that video chats and other lag-sensitive services work as expected. The EFF is also promising ease of use, although you'll have deep control if you're handy with a command prompt.
Just watch out before you leap in. The new firmware only works on Netgear's WNDR3800 so far, and it's characterized as a "hacker alpha release" that will almost certainly be laden with bugs. Really, this is for developers who want to help the EFF fulfill its dreams of creating a best-of-all-worlds WiFi hotspot. If you're one of those tinkerer types, you can check out the project at the source link.