Virtual Wi-Fi was going to be a cool Windows 7 feature to turn PCs into a Wi-Fi access-point, so devices could share a connection without special software. It missed the cut, but this free app finishes the work Microsoft abandoned.
Some of the code that Microsoft Research used to virtualize one Wi-Fi card as several adapters still made its way into Windows 7's underpinnings. Connectify completes the job.
The result is a shared connection that differs to the usual "ad hoc" network connection, because it shows up as a real access point, reverts to default settings each time you restart, and you can join a Wi-Fi network and run the Connectify hotspot on the same Wi-Fi card. Traffic can also be encrypted using WPA-2 Personal (AES).
"You're sitting in a coffee shop that charges you for a wireless connection. With Connectify, I can pay for that connection, and still have all my other devices, like my iPhone, connected to the Internet."